ASTM A490 Bolt Size Chart 2026: Dimensions, Holes & Strength

A490 Bolt Size Chart: Quick Reference

Heavy-hex dimensions, UNC threads and thread length for all nine standard sizes.

How to Read This Chart

Read across a row from nominal diameter to the standard UNC thread, the heavy-hex head width across flats (the wrench or socket size), the basic head height and the nominal structural thread length. A 3/4 in. A490 bolt has a 1-1/4 in. head because heavy-hex structural heads are wider than ordinary hex heads. Head width is a wrench dimension, not the bolt size.

ASTM F3125 Grade A490 heavy-hex structural bolt nominal dimensions per ASME B18.2.6 and RCSC Commentary Table C-2.1. UNC thread designations are the standard coarse series. The 3/4 in. and 1 in. rows are highlighted as common examples, not recommendations.
Nominal diameter	UNC thread	Head across flats	Basic head height	Nominal thread length
1/2 in.	1/2-13 UNC	7/8 in.	5/16 in.	1 in.
5/8 in.	5/8-11 UNC	1-1/16 in.	25/64 in.	1-1/4 in.
3/4 in.	3/4-10 UNC	1-1/4 in.	15/32 in.	1-3/8 in.
7/8 in.	7/8-9 UNC	1-7/16 in.	35/64 in.	1-1/2 in.
1 in.	1-8 UNC	1-5/8 in.	39/64 in.	1-3/4 in.
1-1/8 in.	1-1/8-7 UNC	1-13/16 in.	11/16 in.	2 in.
1-1/4 in.	1-1/4-7 UNC	2 in.	25/32 in.	2 in.
1-3/8 in.	1-3/8-6 UNC	2-3/16 in.	27/32 in.	2-1/4 in.
1-1/2 in.	1-1/2-6 UNC	2-3/8 in.	15/16 in.	2-1/4 in.

Checked against ASME B18.2.6 manufacturer data and RCSC commentary

Chart Notes

Head dimensions are nominal or basic values, not complete manufacturing tolerances. Head width is the wrench dimension, not the nominal bolt diameter. Thread length differs from overall bolt length, and generic heavy-hex thread formulas do not apply to structural bolts. Nonstandard configurations need explicit product specification verification.

ASTM F3125 Grade A490 heavy-hex structural bolt showing nominal diameter, head dimensions, overall length and standard thread length.

Heavy Hex Dimensions

Nine inch diameters from 1/2 to 1-1/2 in. are standard. A490 and A325 bolts of the same diameter share the same head geometry and UNC threads, so dimensions alone cannot tell the grades apart. See the A325 Bolt Size Chart for the Grade A325 data.

UNC Threads and Thread Length

Structural bolts have shorter thread lengths than general-purpose heavy-hex bolts. A 3/4 in. bolt carries 1-3/8 in. of thread no matter how long the bolt is.

What Is an ASTM A490 Structural Bolt?

The Group 150 heavy-hex structural bolt.

An ASTM A490 structural bolt is a high-strength heavy-hex bolt for specified steel-to-steel connections. Type 1 A490 bolts are made from alloy steel (with or without boron), quenched in oil and tempered at not less than 800°F. Bolts in the 150 ksi class also receive magnetic particle inspection and carburization and decarburization testing, which the 120 ksi grades do not.

High-Strength Structural Applications

A490 bolts connect beams, columns, braces, gussets and splice plates where the design calls for the Group 150 strength level, in buildings, industrial frames and bridges.

Heavy Hex Bolt Configuration

The head and nut are heavy hex, and the bolt is supplied with matched nuts and hardened washers. Do not confuse an A490 bolt with a general-purpose bolt or a foundation anchor rod. See the Anchor Bolt Grade Chart for anchor rods.

ASTM A490 vs. ASTM F3125 Grade A490

The old standard, the new standard and how they relate.

ASTM A490 was withdrawn in 2016 and consolidated into ASTM F3125/F3125M, which replaces six standards: A325, A325M, A490, A490M, F1852 and F2280. A490 survives as Grade A490, so the current wording is “ASTM F3125 Grade A490.” ASTM lists F3125/F3125M-26 as the current edition, active as of July 31, 2026, although your project may specify an earlier adopted edition.

Historical ASTM A490

The old standalone specification covered heavy-hex structural bolts of 150 ksi minimum tensile strength from 1/2 through 1-1/2 in., with strict coating restrictions. Many drawings and articles still cite it.

Current ASTM F3125 Specification

F3125 covers bolts in two strength grades (120 and 150 ksi), two types and two styles. Grades A325, A490, F1852 and F2280 are the inch grades. The inch and SI systems are separate, and mixing values from the two can result in nonconformance.

Grade and Material Classification

Classification per ASTM F3125 Table 1 and Section 1.
Item	Grade A490
Minimum strength	150 ksi
Style	Heavy hex
Type 1	Alloy steel or alloy steel with boron
Type 3	Weathering steel
Size range	1/2 to 1-1/2 in.

Checked against ASTM F3125 text

A490 Bolt Diameter Chart

Fractional, decimal and metric values for 1/2 to 1-1/2 in.

The nine standard inch diameters run from 1/2 to 1-1/2 in. Converting an inch diameter to millimeters does not turn an A490 bolt into an A490M metric bolt.

Conversions use exactly 25.4 mm per inch, rounded to two decimals. Maximum body diameter is from ASME B18.2.6.
Nominal diameter	Decimal inches	Millimeters	Body diameter, maximum (in.)
1/2 in.	0.500	12.70	0.515
5/8 in.	0.625	15.88	0.642
3/4 in.	0.750	19.05	0.768
7/8 in.	0.875	22.23	0.895
1 in.	1.000	25.40	1.022
1-1/8 in.	1.125	28.58	1.149
1-1/4 in.	1.250	31.75	1.277
1-3/8 in.	1.375	34.93	1.404
1-1/2 in.	1.500	38.10	1.531

Metric values calculated

Fractional and Decimal Sizes

For general fractional bolt sizes, see the US Bolt Sizes Chart.

Metric Conversions

🧮 Conversion

d_mm = 25.4 × d_in

Example: 3/4 in. = 25.4 × 0.750 = 19.05 mm. These are rounded dimensional conversions, not interchangeable A490M designations. See the Bolt Diameter Chart for general diameters.

Nominal vs. Actual Diameter

Nominal diameter is a designation. A manufactured body is measured within the tolerance in ASME B18.2.6, and the maximum body diameter in the table is slightly above the nominal size.

A490 Heavy Hex Head Dimensions

Why a 3/4 in. bolt needs a 1-1/4 in. wrench.

ASME B18.2.6 gives nominal values and tolerances for the heavy-hex head. A 3/4 in. A490 bolt has a nominal head width of 1-1/4 in. across flats, so the wrench is much larger than the shank. A heavy-hex head is 1/8 in. wider across flats than a standard hex head of the same bolt diameter.

Head dimensions per ASME B18.2.6 (2011 values published by a bolt manufacturer). Check the governing ASME edition before asserting current tolerance compliance.
Bolt	Across flats, basic (in.)	Across flats, max / min (in.)	Across corners, max / min (in.)	Head height, basic (in.)	Head height, max / min (in.)
1/2 in.	7/8	0.875 / 0.850	1.010 / 0.969	5/16	0.323 / 0.302
5/8 in.	1-1/16	1.062 / 1.031	1.227 / 1.175	25/64	0.403 / 0.378
3/4 in.	1-1/4	1.250 / 1.212	1.443 / 1.383	15/32	0.483 / 0.455
7/8 in.	1-7/16	1.438 / 1.394	1.660 / 1.589	35/64	0.563 / 0.531
1 in.	1-5/8	1.625 / 1.575	1.876 / 1.796	39/64	0.627 / 0.591
1-1/8 in.	1-13/16	1.812 / 1.756	2.093 / 2.002	11/16	0.718 / 0.658
1-1/4 in.	2	2.000 / 1.938	2.309 / 2.209	25/32	0.813 / 0.749
1-3/8 in.	2-3/16	2.188 / 2.119	2.526 / 2.416	27/32	0.878 / 0.810
1-1/2 in.	2-3/8	2.375 / 2.300	2.742 / 2.622	15/16	0.974 / 0.902

Width Across Flats

This is the wrench size. A 1 in. A490 bolt has a 1-5/8 in. head across flats, so it needs a 1-5/8 in. socket or wrench.

Width Across Corners

The corner-to-corner width governs tool and edge clearance and is larger than the across-flats value.

Head Height and Tolerances

The basic head height is a nominal reference. Real heads fall between the minimum and maximum shown.

A490 Bolt Thread Size and Pitch

UNC coarse threads and the pitch formula.

A490 bolts use the Unified National Coarse (UNC) series with a 2A thread fit. The number after the hyphen is threads per inch (TPI).

UNC Thread Chart

Pitch is calculated as 1/TPI. Tensile stress areas are the standard values listed in ASTM F3125 for each size.
Bolt	UNC thread	Threads per inch	Pitch (in.)	Pitch (mm)	Tensile stress area (in²)
1/2 in.	1/2-13	13	0.0769	1.95	0.142
5/8 in.	5/8-11	11	0.0909	2.31	0.226
3/4 in.	3/4-10	10	0.1000	2.54	0.334
7/8 in.	7/8-9	9	0.1111	2.82	0.462
1 in.	1-8	8	0.1250	3.17	0.606
1-1/8 in.	1-1/8-7	7	0.1429	3.63	0.763
1-1/4 in.	1-1/4-7	7	0.1429	3.63	0.969
1-3/8 in.	1-3/8-6	6	0.1667	4.23	1.155
1-1/2 in.	1-1/2-6	6	0.1667	4.23	1.405

Pitch calculated

Thread Pitch Formula

🧮 Pitch

P_in = 1 / TPIP_mm = 25.4 / TPI

3/4-10 UNC example: P = 1/10 = 0.100 in. = 2.54 mm. For thread identification, see the UNC Thread Chart, Thread Size Chart and Thread Pitch Chart.

UNC Is Not Metric

A 3/4-10 UNC bolt is not interchangeable with an M20 metric thread. The pitches (2.54 mm and 2.5 mm) and diameters (19.05 mm and 20 mm) are close but different, so mixed hardware will not fit or perform correctly.

A490 Structural Bolt Thread Length

Shorter than a general-purpose heavy-hex bolt, by design.

Structural bolts use a standardized short thread length. It keeps the plain shank in the shear plane when grip is controlled, which is why thread length differs from the general-purpose formula. Standard A490 structural bolts are not fully threaded, and a fully threaded A490 is not a standard product.

Standard Thread Length

Structural values per ASME B18.2.6 and RCSC Commentary Table C-2.1. General values from ASME B18.2.1 for bolts up to 6 in. long. Do not use the general formula for F3125 structural bolts.
Bolt	Structural thread length (in.)	General heavy hex, 6 in. or less (2D + 1/4) (in.)
1/2 in.	1	1.25
5/8 in.	1-1/4	1.50
3/4 in.	1-3/8	1.75
7/8 in.	1-1/2	2.00
1 in.	1-3/4	2.25
1-1/8 in.	2	2.50
1-1/4 in.	2	2.75
1-3/8 in.	2-1/4	3.00
1-1/2 in.	2-1/4	3.25

General-bolt column calculated

Threaded and Unthreaded Shank

Overall bolt length, thread length, unthreaded body and the thread transition are four different things. Thread length does not change with bolt length, so a 3/4 × 3-1/4 bolt and a 3/4 × 5 bolt both have 1-3/8 in. of thread.

Shear Plane Considerations

Whether the shear plane crosses threads (N) or the plain shank (X) changes the design shear strength. Bolts with thread lengths or dimensions that differ from the specification may be ordered under A354 or A449, but ASTM notes those are not exact equivalents. A fully threaded variant marked “T” exists only for A325, and nonstandard dimensions are marked “S”. Do not assume fully threaded A490 bolts are standard products.

A490 Bolt Length and Grip Selection

Grip, washers and allowances decide the length.

Nominal bolt length is measured from under the head to the end of the bolt, so it excludes head height. The required length is the grip plus washers plus a tabulated allowance for the nut and thread projection. Length selection also depends on thread configuration and length tolerances.

Measuring Bolt Length

🧮 Required Bolt Length

L_required = G + t_components + a_d

Variables: G = steel grip (total connected thickness, no washers), t_components = separately counted washers and indicators (5/32 in. per ordinary F436 washer, 5/16 in. per beveled washer), a_d = allowance for the bolt diameter. Round up to the next 1/4 in. (1/2 in. above 6 in.).

Grip and Washer Allowances

Allowance excludes washers, which are counted separately.
Bolt diameter	Added length a_d (in.)
1/2 in.	11/16
5/8 in.	7/8
3/4 in.	1
7/8 in.	1-1/8
1 in.	1-1/4
1-1/8 in.	1-1/2
1-1/4 in.	1-5/8
1-3/8 in.	1-3/4
1-1/2 in.	1-7/8

RCSC Commentary Table C-2.2

Worked Length Example

1

Selecting a 3/4 in. A490 Bolt

Given: Total steel grip G = 2.00 in., one F436 washer (5/32 in.), 3/4 in. bolt with allowance 1 in.

1

Add: L = 2 + 5/32 + 1 = 3.15625 in.

2

Round up to the next 1/4 in.: 3-1/4 in.

Result: preliminary selection 3/4 × 3-1/4 in.

What it means: Verify available lengths, thread engagement and the assembly components. The bolt end must be flush with or beyond the nut face.

A490 structural bolt grip length, washer allowance, nut engagement and overall bolt length.

Do not assume every A490 bolt has the same thread position for every nominal length. Length tolerances are minus values: up to 6 in., 1/2 and 5/8 in. bolts are up to 0.12 in. short, 3/4 to 1 in. up to 0.19 in. short and 1-1/8 to 1-1/2 in. up to 0.25 in. short. Plate dimensions for grip come from the Steel Plate Thickness Chart.

A490 Type 1 vs. Type 3

Alloy steel or weathering steel, same size and strength group.

Type 1 and Type 3 are material classifications. Both follow the Grade A490 strength level and the heavy-hex dimensions.

Per ASTM F3125 Table 2 and Section 6.
Property	Type 1	Type 3
Material	Alloy steel or alloy steel with boron	Weathering steel
Nominal geometry	Standard A490 dimensions	Standard A490 dimensions
Strength group	Group 150	Group 150
Chemistry basis	Composition limits in F3125	Composition A or B, or a corrosion index of 6 or greater
Nuts	A563 Grade DH	A563 Grade DH3
Washers	F436 Type 1	F436 Type 3

Alloy Steel and Weathering Steel

Type 3 is weathering steel designed to form a protective patina in suitable wet-dry outdoor exposure. It is not stainless steel, and it does not remove the need to evaluate the exposure conditions. Type 3 assemblies use matching Type 3 nuts and washers.

A490 Mechanical Properties

Tensile and yield strength, hardness and testing.

F3125 sets the mechanical requirements for Grade A490. The values below come from the specification tables for machined specimens and hardness.

Values from ASTM F3125 (edition reviewed: 2021). Confirm against F3125/F3125M-26 and the manufacturer certification for your project.
Property	Requirement
Minimum tensile strength	150 ksi
Maximum tensile strength	173 ksi
Minimum yield strength	130 ksi
Elongation in 4D, minimum	14 percent
Reduction of area, minimum	40 percent
Hardness, Brinell	311 to 352 HB
Hardness, Rockwell C	33 to 38 HRC

Checked against ASTM F3125 tables 6 and 7

Heat Treatment and Testing

Bolts are quenched in oil and tempered at not less than 800°F. Each lot is tested for tensile strength, proof load and hardness. The 150 ksi grades also get magnetic particle inspection and carburization and decarburization checks, and manufacturers provide test reports when specified.

Material Strength Is Not Connection Strength

The 150 ksi minimum tensile strength is a material specification value. It is not the allowable load of a bolt or a connection. Bolt shear, bolt tension, pretension and connected-plate limit states are separate checks.

A490 Bolt Hole Size Chart

Standard, oversize and slotted holes from RCSC Table 3.1.

RCSC 2025 Table 3.1 lists nominal hole dimensions. Standard holes are 1/16 in. larger than the bolt through 7/8 in. and 1/8 in. larger from 1 in. up. These are structural steel holes. They are not concrete anchor drill-bit sizes or general machine-bolt clearance holes, which are covered in the Clearance Hole Size Chart.

Nominal dimensions from RCSC 2025 Table 3.1. For 1-1/8 in. and larger: standard d + 1/8, oversized d + 5/16, short slot (d + 1/8) × (d + 3/8), long slot (d + 1/8) × 2.5d (calculated). Permitted hole types depend on the governing connection design.
Bolt diameter	Standard hole	Oversized hole	Short slot (width × length)	Long slot (width × length)
1/2 in.	9/16 in.	5/8 in.	9/16 × 11/16 in.	9/16 × 1-1/4 in.
5/8 in.	11/16 in.	13/16 in.	11/16 × 7/8 in.	11/16 × 1-9/16 in.
3/4 in.	13/16 in.	15/16 in.	13/16 × 1 in.	13/16 × 1-7/8 in.
7/8 in.	15/16 in.	1-1/16 in.	15/16 × 1-1/8 in.	15/16 × 2-3/16 in.
1 in.	1-1/8 in.	1-1/4 in.	1-1/8 × 1-5/16 in.	1-1/8 × 2-1/2 in.
1-1/8 in.	1-1/4 in.	1-7/16 in.	1-1/4 × 1-1/2 in.	1-1/4 × 2-13/16 in.
1-1/4 in.	1-3/8 in.	1-9/16 in.	1-3/8 × 1-5/8 in.	1-3/8 × 3-1/8 in.
1-3/8 in.	1-1/2 in.	1-11/16 in.	1-1/2 × 1-3/4 in.	1-1/2 × 3-7/16 in.
1-1/2 in.	1-5/8 in.	1-13/16 in.	1-5/8 × 1-7/8 in.	1-5/8 × 3-3/4 in.

Checked against RCSC Table 3.1 1-1/8 in. and larger calculated from table formulas

Standard Holes

2

Hole Clearance Example

Given: 3/4 in. bolt, standard hole of 13/16 in.

1

Diametral difference: Δd = 13/16 − 3/4 = 1/16 in.

2

Ideal radial clearance: c_r = (1/16) / 2 = 1/32 in.

Result: 1/16 in. diametral and 1/32 in. radial (ideal).

What it means: Radial clearance is an ideal concentric geometry result, not a manufacturing tolerance.

Oversized Holes

Used only where the joint type and design permit, and they are not interchangeable with standard holes.

Short and Long Slots

Slots allow adjustment. The slot direction, which plies may be slotted and the washer requirements come from RCSC and the connection design.

A490 Bolt Spacing and Edge Distance

AISC minimums and why diameter alone is not enough.

Bolt diameter alone does not set the hole layout. AISC requires a minimum center-to-center spacing of 2⅔ bolt diameters and prefers 3d. Edge distance runs from the center of a hole to the edge of the connected part, and end distance is the same measurement in the direction of force. Hole type, plate thickness, bearing, tearout and the bolt group geometry all matter.

Spacing calculated from the AISC rule. Edge distances from AISC Table J3.4 for standard holes. Oversize and slotted holes add an increment. Check your adopted edition.
Bolt	Minimum spacing 2⅔d	Preferred spacing 3d	Min. edge at sheared edge (standard hole)	Min. edge at rolled or thermally cut edge
1/2 in.	1-1/3 in.	1-1/2 in.	7/8 in.	3/4 in.
5/8 in.	1-2/3 in.	1-7/8 in.	1-1/8 in.	7/8 in.
3/4 in.	2 in.	2-1/4 in.	1-1/4 in.	1 in.
7/8 in.	2-1/3 in.	2-5/8 in.	1-1/2 in.	1-1/8 in.
1 in.	2-2/3 in.	3 in.	1-3/4 in.	1-1/4 in.

Spacing calculated Edge distance: AISC Table J3.4

Center-to-Center Spacing

For a 3/4 in. bolt the minimum is 2 in. and the preferred spacing is 2-1/4 in. For layout help, see the Bolt Pattern Calculator.

Edge and End Distance

Values depend on hole type and edge condition. Do not publish one universal spacing or edge rule as a complete design method.

Connected Steel Requirements

A correct bolt diameter does not guarantee adequate plate bearing, tearout or block shear. Check plate sizes in the Steel Plate Thickness Chart.

A490-Compatible Nuts

Nut grade and style matter as much as thread size.

F3125 recommends ASTM A563 Grade DH heavy-hex nuts for Type 1 A490 bolts and Grade DH3 for Type 3. An ASTM A194 Grade 2H heavy-hex nut may replace a DH nut on Type 1 A490 bolts. If coated 2H nuts are used, the same coating, thread and lubrication requirements apply as for DH nuts. An ordinary nut with matching thread diameter is not automatically acceptable.

Per ASTM F3125 Table 2. RCSC and the project specification govern the exact assembly.
A490 bolt	Recommended nut	Suitable alternative	Washer
Type 1	ASTM A563 Grade DH	ASTM A194 Grade 2H	F436 Type 1
Type 3	ASTM A563 Grade DH3	Per ASTM F3125 and RCSC	F436 Type 3

Checked against ASTM F3125 Table 2

ASTM A563 and Alternatives

DH nuts match A490 strength. Bolt, nut and washer should be supplied and used as a matched assembly.

Heavy Hex Nut Dimensions

Heavy-hex nuts share the head width across flats shown above. Nominal nut thicknesses include 39/64 in. for 5/8 in., 47/64 in. for 3/4 in. and 55/64 in. for 7/8 in. See the Nut Size Chart for general nut dimensions.

Thread and Coating Compatibility

The nut thread must match the bolt UNC thread, and F3125 requires bolts and nuts to be coated by the same process, with no mixed processes in a lot.

A490 Hardened Washer Requirements

F436 washers and where they go.

ASTM F436/F436M hardened washers are used with A490 assemblies, Type 1 washers with Type 1 bolts and Type 3 washers with Type 3 bolts. Where washers go depends on the joint, the installation method, the hole type and the component configuration. RCSC Section 6 sets the requirements, and the 2025 edition adds ASTM F3394 backup and reaction washers.

Nominal inside and outside diameters from F436 round washer data. Thickness is a range. Confirm against the current F436/F436M table.
Bolt size (in.)	Inside diameter (in.)	Outside diameter (in.)	Thickness (in.)
1/2	0.531	1.063	0.097 to 0.177
5/8	0.688	1.313	0.122 to 0.177
3/4	0.812	1.469	0.122 to 0.177
7/8	0.938	1.750	0.136 to 0.177
1	1.125	2.000	0.136 to 0.177
1-1/8	See ASTM F436	See ASTM F436	See ASTM F436
1-1/4	1.375	2.500	0.136 to 0.177
1-3/8	1.531	2.750	0.136 to 0.177
1-1/2	1.625	3.000	0.136 to 0.177

ASTM F436 Washers and Placement

For other washer types, see the Washer Size Chart.

Special Hole Configurations

Oversized and slotted holes can need washers or plate washers that a snug-tightened standard-hole joint does not. Check RCSC for the exact requirement.

A490 Bolt Head Markings

Grade, manufacturer and traceability.

F3125 requires the grade and type marking and the manufacturer’s mark on the bolt head, in separate and distinct locations. Heavy-hex A490 bolts are marked “A490,” and twist-off F2280 assemblies carry an “A490TC” or alternate “A490” mark. Marking must remain visible after coating, and Type 3 bolts may carry additional distinguishing marks at the manufacturer’s option.

Grade identification: the A490 mark on the head.
Manufacturer markings: the maker’s mark.
Traceability: each lot has a unique lot number, test reports and package marking (grade, type, style, size and lot).

Markings Need Documentation

Head markings alone do not demonstrate every part of specification compliance. For 150 ksi bolts, the manufacturer’s test report also includes the certification that any coating has been qualified for use on 150 ksi bolts, including hydrogen embrittlement testing.

Illustration comparing four nominal sizes of A490 heavy-hex structural bolts with identification markings, threaded shanks, a heavy-hex nut, washers and a measuring ruler. — ASTM F3125 Grade A490 high-strength structural bolts feature heavy-hex heads, identification markings and standard structural threading.

A490 Minimum Bolt Pretension

Group 150 values from the 2025 RCSC specification.

RCSC 2025 Table 5.2 gives the specified minimum bolt pretension for pretensioned and slip-critical joints. Group 144 and Group 150 share one column, which is the A490 column. A 3/4 in. A490 bolt has a minimum specified pretension of 35 kips for those joint conditions.

Group 150 Pretension Chart

Specified minimum bolt pretension from RCSC 2025 Table 5.2 for pretensioned and slip-critical joints. These are not torque settings.
Nominal diameter	Minimum pretension, Group 150
1/2 in.	15 kips
5/8 in.	24 kips
3/4 in.	35 kips
7/8 in.	49 kips
1 in.	64 kips
1-1/8 in.	80 kips
1-1/4 in.	102 kips
1-3/8 in.	121 kips
1-1/2 in.	148 kips

Checked against RCSC 2025 Table 5.2

Pretension vs. Strength

Minimum pretension is a clamping requirement. It is not bolt tensile resistance, a failure load or the allowable load of the connection.

Verification Requirements

RCSC requires pre-installation verification testing of the bolting assembly, the pretensioning method and the tools, using a bolt tension measuring device (BTMD).

TOOLS & EQUIPMENT

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A490 Bolt Torque vs. Pretension

Why a torque value does not tell you the bolt tension.

No universal torque chart can guarantee the specified A490 pretension. Most wrench effort goes into friction at the threads and under the nut, and the friction varies with coating, lubrication, thread condition and handling. A simplified relationship is:

🧮 Torque and Clamping Force

T = K × F × d

Variables: T = applied torque, K = approximate nut factor, F = axial clamping force, d = nominal bolt diameter. K changes with friction, coating, lubrication and assembly condition, so do not recommend an installation torque from an assumed K. For general-purpose torque references, see the Bolt Torque Chart and Bolt Torque Calculator. Those are not RCSC procedures.

Torque and Friction

For the same tension, a higher nut factor needs proportionally more torque. Lubricants, coatings, reuse and weather exposure all shift the result.

Installation Methods and RCSC Requirements

RCSC 2025 recognizes the turn-of-nut method, the twist-off tension-control bolt method, the direct tension indicator method and the combined method. The calibrated wrench method was withdrawn in the 2025 edition. The combined method still uses a calibrated wrench for the initial torque followed by a specified rotation.

A490 Structural Joint Types

Snug-tightened, pretensioned and slip-critical.

RCSC defines three joint types. Which one applies is a structural design decision that appears on the drawings.

N = threads included in the shear plane. X = threads excluded. SC = slip-critical. These describe the connection, not different A490 grades.
Joint type	Primary concept	Design designation
Snug-tightened	Plies brought into firm contact, with the tightness from a few impacts of an impact wrench or the full effort of an ironworker with a spud wrench	N or X (bearing)
Pretensioned	Bolt installed to the specified minimum pretension	N or X (bearing)
Slip-critical	Pretensioned with prepared faying surfaces, designed to resist slip	SC

Snug-Tightened

Bolts carry shear by bearing against the hole. Snug-tightened bolts are not free of tension, and the joint type is not allowed for every condition.

Pretensioned

Pretension is required in specified conditions under RCSC and AISC. Not every A490 joint must be pretensioned.

Slip-Critical

Slip resistance depends on the clamping force and the faying-surface condition. Connection classification is determined by the structural design requirements.

A490 Bolt Shear Strength

Nominal bolt shear, one plane at a time.

Nominal shear strength per bolt per shear plane is the nominal shear stress times the gross bolt area. In AISC 360-16 Table J3.2, Group B (A490) bolts use 68 ksi with threads included in the shear plane (N) and 84 ksi with threads excluded (X). Use the current table for your edition. Rounded and unrounded stress values (for example 68 ksi versus 67.5 ksi) differ by under 1 percent.

Bolt Area

🧮 Area and Shear

A_b = π d² / 4R_n = F_nv × A_b

Variables: A_b = gross bolt area (in²), F_nv = nominal shear stress (ksi), R_n = nominal shear strength per shear plane (kips).

Thread Location

Illustrative values calculated from F_nv × A_b. Not design values for a complete connection.
Bolt	Gross area A_b (in²)	R_n threads included (68 ksi), kips	R_n threads excluded (84 ksi), kips
1/2 in.	0.1963	13.35	16.49
5/8 in.	0.3068	20.86	25.77
3/4 in.	0.4418	30.04	37.11
7/8 in.	0.6013	40.89	50.51
1 in.	0.7854	53.41	65.97
1-1/8 in.	0.9940	67.59	83.50
1-1/4 in.	1.2272	83.45	103.08
1-3/8 in.	1.4849	100.97	124.73
1-1/2 in.	1.7671	120.17	148.44

Calculated

Worked Shear Example

3

3/4 in. A490 Bolt in Single Shear

Given: 3/4 in. bolt, one shear plane, threads included, F_nv = 68 ksi, LRFD resistance factor φ = 0.75.

1

Area: A_b = (0.75)² π/4 = 0.4418 in²

2

Nominal strength: R_n = 68 × 0.4418 = 30.04 kips

3

Design strength: φR_n = 0.75 × 30.04 = 22.53 kips

Result: 30.04 kips nominal and 22.53 kips LRFD for one bolt in one shear plane.

What it means: This is an individual bolt illustration, not the capacity of the connection. Joint length, single or double shear, bearing, tearout, block shear and net section also apply.

A490 Bolt Tensile Strength

Nominal tension, and why 150 ksi is not the design stress.

Use the structural design tensile stress, not the material minimum tensile strength. For Group 150 bolts in AISC 360-16 the nominal tensile stress is 113 ksi, while the material minimum tensile strength is 150 ksi.

Nominal Tensile Resistance

🧮 Nominal Tension

R_n = F_nt × A_b

Variables: F_nt = nominal tensile stress (113 ksi for Group 150 in this example), A_b = gross bolt area.

Worked Tension Example

4

3/4 in. A490 Bolt in Tension

Given: 3/4 in. bolt, F_nt = 113 ksi, φ = 0.75.

1

Nominal: R_n = 113 × 0.4418 = 49.92 kips

2

Design: φR_n = 0.75 × 49.92 = 37.44 kips

Result: 49.92 kips nominal and 37.44 kips LRFD.

What it means: This is not a universal safe working load. It ignores prying and connected-material failure modes.

Combined Loading

Shear and tension often act together, and AISC Chapter J requires an interaction check. Prying action can add tension, and plate failure modes can control before the bolt does.

A490 vs. A325 Structural Bolts

Group 150 against Group 120.

A490 and A325 are different grades in the same F3125 specification. Compare the grade data here and see the A325 Bolt Size Chart for the Grade A325 details.

Mechanical values from ASTM F3125; pretension from RCSC 2025 Table 5.2.
Property	A325	A490
RCSC strength group	Group 120	Group 150
Minimum tensile strength	120 ksi	150 ksi
Minimum yield strength	92 ksi	130 ksi
Standard head geometry	Heavy hex	Heavy hex
Common thread series	UNC	UNC
3/4 in. minimum pretension	28 kips	35 kips
1 in. minimum pretension	51 kips	64 kips
Nominal diameter range	1/2 to 1-1/2 in.	1/2 to 1-1/2 in.
Material types	Type 1, Type 3	Type 1, Type 3
Nuts	A563 DH, or other permitted grades	A563 DH or A194 2H (Type 1)

Comparison of ASTM F3125 Grade A325 and Grade A490 strength classifications and minimum pretension for a 3/4 in. bolt.

Selection and Substitution

Higher strength does not automatically justify substitution. Switching grades can change the design resistance, the required pretension, the nuts and washers, the coatings and the inspection requirements. Do not substitute without design and specification approval. For the broad grade comparison, see the Bolt Grade Chart and the Structural Bolt Size Chart.

A490 vs. ASTM A354 Grade BD

When a bolt with A490-level strength needs a different configuration.

ASTM A354 Grade BD is a quenched and tempered alloy steel bolt grade with mechanical properties equal to A490. Unlike A490, A354 is not restricted to heavy-hex structural geometry, so it is used where the F3125 configuration does not fit: nonstandard thread lengths, other head styles, threaded rods and anchor bolts, and diameters above 1-1/2 in. F3125 itself says bolts with different thread lengths or dimensions may be ordered under A354 or A449, and warns that these are not exact equivalents to the structural grades.

A354 values from manufacturer technical data; F3125 values from ASTM F3125. Check the current standards for your project.
Topic	F3125 Grade A490	ASTM A354 Grade BD
Scope	Heavy-hex structural bolts and assemblies	Quenched and tempered alloy steel bolts, studs and threaded fasteners
Size range	1/2 to 1-1/2 in.	1/4 to 2-1/2 in. for BD (up to 4 in. under A354)
Minimum tensile strength	150 ksi (173 ksi maximum)	150 ksi (173 ksi maximum)
Minimum yield strength	130 ksi	130 ksi
Configuration	Heavy hex, standard structural thread length	Unrestricted
Magnetic particle test	Required for 150 ksi bolts	Not required unless a supplemental requirement is called out

Product Specification and Thread Configuration

A354 BD is considered when nonstandard thread configurations are required, and the A354 text notes that for structural bolting above 1-1/2 in., F3125 requirements such as head size, lubricant and magnetic particle inspection should be carefully considered.

Structural Use Limitations

Do not describe A354 Grade BD as automatically equivalent to F3125 Grade A490 in structural joints. A change of specification needs engineering approval.

A490 Coatings and Hydrogen Embrittlement

The most important difference from A325.

Coatings are the biggest practical difference between A490 and A325. At 150 ksi, A490 is susceptible to hydrogen embrittlement, so hydrogen introduced by plating or pickling can cause delayed brittle fracture. That is why A490 coating rules are stricter than A325 rules.

Coating Restrictions

The old standalone A490 specification prohibited hot-dip galvanizing, mechanical deposition and electroplating with zinc. Under current F3125, Annex A1 lists the permitted coatings, and both hot-dip galvanizing (ASTM F2329) and mechanical galvanizing (ASTM B695) are shown as not qualified for Grade A490 bolts. Any coating that is not an approved system is not permitted.

Qualified Coating Systems

Zinc/aluminum corrosion-protective coatings have long been the approved route, for example ASTM F1136 Grade 3 (commercially known as Geomet). Current F3125 requires coatings for 150 ksi bolts to be qualified under IFI 144, including hydrogen embrittlement testing to ASTM F1940 (internal) and F2660 (environmental). The manufacturer’s test report must certify this. Confirm the permitted list in Annex A1 of the edition governing your project.

Summary only. Verify against F3125 Annex A1 and RCSC for the edition in force.
Coating or finish	Status for Grade A490	Basis
Plain finish	Permitted	Default if nothing is specified
Hot-dip galvanizing (F2329)	Not qualified	F3125 Annex A1
Mechanical galvanizing (B695)	Not qualified	F3125 Annex A1
Electroplated zinc	Prohibited	Hydrogen embrittlement risk
Zinc/aluminum corrosion-protective coating (F1136 Grade 3)	Approved when qualified	Long-standing approved route
Other coating systems	Only if qualified under IFI 144 with F1940 and F2660 testing	F3125 coating qualification

Weathering Steel and Assembly Compatibility

Type 3 A490 bolts are weathering steel and rely on the patina instead of a coating. Bolts and nuts must be coated by the same process, and the nut and washer must match the coating system. For slip-critical joints, coatings on the faying surfaces are a separate qualification issue. A325 bolts have wider coating options, so do not apply A325 coating practice to A490.

A490 Bolt Applications

Where Group 150 bolts are used in steel construction.

A490 bolts are used where the design calls for the Group 150 strength level.

Beam connections: beam-to-column connections and shear tabs. See the Steel I-Beam Chart and Steel Beam Size Chart.
Bracing and splices: splice plates, gussets and braces, including tube members in the HSS Size Chart.
Industrial and bridge structures: heavy frames, and bridge connections where specified.
High-strength joints: connections of the members in the Structural Steel Shapes Chart.

A490 is not a general replacement for concrete anchor rods or for every high-strength machine bolt. For welded alternatives, see the Fillet Weld Size Chart.

Close-up of a steel I-beam connected to a structural column with connection plates, A490-marked heavy-hex bolt heads, and washers. — Structural steel beam-to-column connection featuring A490-marked high-strength bolts arranged on steel connection plates. ASTM F3125 Grade A490 bolts are used in structural steel applications requiring high-strength fastening.

How to Measure and Identify an A490 Bolt

A practical identification sequence.

Use this sequence to identify and measure an A490 bolt.

Identify head markings. Look for the A490 grade mark and the manufacturer mark.
Measure nominal diameter. Use calipers on the unthreaded shank.
Measure heavy-hex width across flats. Compare with the chart, for example 1-1/4 in. for a 3/4 in. bolt.
Measure under-head bolt length. Do not include the head.
Determine UNC thread pitch. A thread gauge should show the UNC pitch, such as 10 TPI for a 3/4 in. bolt.
Check the structural thread length.
Confirm material type and finish.
Review certification and traceability. Test reports confirm what the head cannot.

For diameter and thread details, see the chart at the top of this page and the Bolt Diameter Chart.

How to Select the Correct A490 Bolt Size

Follow the drawings, then check each component.

The diameter comes from the engineered design, not from this chart.

Read the approved structural drawings.
Identify the specified Grade A490 and the product type.
Determine the required diameter.
Check the hole type and dimensions.
Determine the grip and the bolt length.
Confirm the nuts and washers.
Verify coating compatibility.
Identify the joint installation requirements.
Check inspection and certification requirements.

No Unapproved Substitution

Do not substitute grade or size without approval from the engineer of record. For the wider family of structural bolts, see the Structural Bolt Size Chart.

A490 Installation and Inspection

Methods, verification and reuse.

Install and inspect A490 bolts under the project specification and RCSC. Do not use a generic torque instruction.

Before Installation

Handle and store assemblies to keep them clean and lubricated, match bolts, nuts and washers by lot, and confirm the test reports and coating certification.

Pretensioning and Verification

Where pretension is specified, use an approved RCSC method (turn-of-nut, twist-off tension control, direct tension indicator or combined method) after pre-installation verification testing. Calibrated-wrench installation was withdrawn in the 2025 edition. Snug-tightening applies only where the design allows it.

Inspection and Reuse

Inspection follows the joint type. Nonconforming assemblies have a defined remedy, and bolt reuse is restricted and depends on grade, finish and joint type, so check RCSC Section 2.11 before reusing any A490 bolt.

Construction worker operating a hydraulic bolt tensioner on an A490-marked structural steel connection with an ENERPAC hydraulic pump and pressure gauge. — A construction worker uses hydraulic bolt-tensioning equipment on a steel beam-to-column connection featuring A490-marked structural bolts. The image illustrates hydraulic equipment used in controlled fastening operations.

Common A490 Bolt Mistakes

The dimension, coating and installation errors that cause the most trouble.

Outdated specification

Treating withdrawn standalone ASTM A490 as the current specification.

Dimension errors

Confusing head width with nominal diameter, measuring length over the head, or using general-purpose heavy-hex thread lengths.

Wrong hardware

Using incompatible UNC and metric hardware, or ordinary nuts and washers.

Coating mistakes

Assuming all zinc coatings are acceptable, or ignoring hydrogen embrittlement.

Type confusion

Treating Type 3 as stainless steel.

Pretension confusion

Confusing pretension with torque, or assuming every joint requires pretension.

Strength misuse

Using minimum tensile strength as an allowable load.

Shear plane errors

Ignoring threads in the shear plane.

Hole restrictions

Ignoring bolt-hole restrictions.

Grade substitution

Substituting A490 for A325 without approval.

Connected steel

Ignoring plate bearing, tearout and block shear.

Reuse

Reusing installed bolts without checking the rules.

A490 Chart Limitations and Structural Safety

Reference dimensions are not a connection design.

This chart provides dimensional and technical reference data. It does not independently establish:

The correct bolt diameter for a new connection.
Complete connection capacity or bolt group strength.
The required number of bolts or safe hole spacing.
Slip resistance.
Approved coating substitution.
Installation acceptance or structural design compliance.

The structural drawings, the Engineer of Record, the applicable standards and the project requirements control. Calculated and illustrative values are labeled. RCSC values are in U.S. Customary units, and RCSC strongly discourages direct conversion to SI.

A490 Bolt Size FAQs

Straight answers to the most common A490 bolt questions.

What sizes do A490 bolts come in?

Grade A490 heavy-hex bolts are furnished in nine inch sizes from 1/2 to 1-1/2 in. The metric A490M runs from M12 to M36. Standard thread lengths are listed in the chart above.

What replaced ASTM A490?

ASTM F3125/F3125M replaced the standalone A490 specification in 2016. A490 is now Grade A490 within F3125.

What is ASTM F3125 Grade A490?

It is the 150 ksi class heavy-hex structural bolt grade in ASTM F3125/F3125M, made of alloy steel (Type 1) or weathering steel (Type 3).

What is the head size of a 3/4-inch A490 bolt?

The nominal head is 1-1/4 in. across flats and 15/32 in. high.

What wrench size fits a 1-inch A490 bolt?

The head is 1-5/8 in. across flats, so a 1-5/8 in. wrench or socket fits. For tool sizes, see the Nut Size Chart.

What UNC threads do A490 bolts use?

UNC coarse threads: 1/2-13, 5/8-11, 3/4-10, 7/8-9, 1-8, 1-1/8-7, 1-1/4-7, 1-3/8-6 and 1-1/2-6.

Are A490 bolts fully threaded?

Standard structural A490 bolts are not fully threaded. They have a shortened structural thread length, such as 1-3/8 in. on a 3/4 in. bolt. Fully threaded A490 is not a standard product.

What hole size is required for a 3/4-inch A490 bolt?

A standard hole is 13/16 in. and an oversized hole is 15/16 in., per RCSC 2025 Table 3.1.

What is the tensile strength of an A490 bolt?

The minimum tensile strength is 150 ksi, with a 173 ksi maximum and a 130 ksi minimum yield strength. These are material values, not connection capacity.

What is the minimum pretension for a 3/4-inch A490 bolt?

35 kips for pretensioned and slip-critical joints under RCSC 2025.

Is A490 stronger than A325?

A490 has a higher minimum tensile strength (150 ksi against 120 ksi), and a higher minimum pretension. See the A325 Bolt Size Chart.

Can A490 replace A325?

Not automatically. Substitution changes the design resistance, pretension, hardware, coating selection and inspection, so it needs design and specification approval.

Can A490 bolts be galvanized?

Hot-dip and mechanical galvanizing are not qualified for Grade A490 because of hydrogen embrittlement, and electroplating is prohibited. Qualified zinc/aluminum coating systems are the approved route. Check F3125 Annex A1.

What is the difference between Type 1 and Type 3?

Type 1 is alloy steel. Type 3 is weathering steel. They share the same sizes and strength level, and neither is stainless steel.

What nuts and washers are required?

ASTM A563 Grade DH heavy-hex nuts (or A194 Grade 2H on Type 1 bolts) and ASTM F436 Type 1 hardened washers. Type 3 bolts use DH3 nuts and Type 3 washers.

Can A490 bolts be reused?

Reuse is restricted and depends on the grade, finish and joint type. RCSC Section 2.11 sets the rules.

How do I select A490 bolt length?

Add the grip, the washer thicknesses and the diameter allowance, then round up to the next 1/4 in. A 2 in. grip with one washer on a 3/4 in. bolt gives a preliminary 3-1/4 in. length.

Are A490 bolts suitable for concrete anchoring?

No. Grade A490 structural bolts are for steel-to-steel joints. Foundation anchor rods follow a different standard. See the Anchor Bolt Grade Chart.

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Sources and Standards Used

Dimensions come from ASME B18.2.6 as published by a bolt manufacturer. Hole sizes and pretension follow the 2025 RCSC Specification. Mechanical properties, nut and washer pairings and the coating framework follow ASTM F3125, using the text of the 2021 edition, so confirm details against F3125/F3125M-26. Pitch, metric conversions, general-bolt thread lengths and illustrative shear and tension values are calculated and marked as derived.

ASTM A490 Bolt Size Chart: Dimensions, Holes & Strength

Key Facts