Common U-Bolt Dimensions

These are specific commercial product dimensions, not universal ASME dimensions for every U-bolt. Verify the selected manufacturer’s drawing. Fastenal lists several rod sizes for some pipe sizes; this table shows the 3/8 in. rod through 4 in. and the 1/2 in. rod for 6 and 8 in. The full list is in the rod diameter section below.

Rod Diameter

D is the diameter of the steel rod and usually the nominal thread diameter.

Inside Width

C is the clear distance between the two legs, measured between the inner faces.

Inside Length

L is the inside dimension from the bend toward the leg ends, following the manufacturer’s stated reference.

Thread Length

T is the length of the usable threaded leg. Fastenal lists it as a reference value.

1. Measure the rod diameter D across one leg.
2. Measure the clear inside width C between the inner leg faces.
3. Measure the inside length L from the inside bend reference to the leg-end reference.
4. Measure the threaded length T.
5. Determine the thread pitch with a thread gauge. The Thread Identification Chart helps.
6. Identify the bend style, round or square.
7. Identify the coating and material where relevant.

Pipe U-bolts are often sold by nominal pipe size, but fit depends on the actual pipe outside diameter and the U-bolt’s manufactured inside width. The table below lists the sizes with every dimension, with the pipe’s actual OD for comparison. For the full pipe OD reference, see the Pipe Outside Diameter Chart.

For 3, 3-1/2 and 4 in. pipe, the Fastenal inside width equals the pipe OD, within the listed tolerance. A rule that C must be larger than the pipe does not hold for every product, so rely on the manufacturer’s drawing and tolerance.

Nominal pipe size is a naming system, not a direct measurement of OD. In the Fastenal series, a U-bolt sold for 2-in. pipe has an inside width of 2-1/2 in., while the 2-in. pipe OD is 2.375 in. Do not conclude that every 2-in. pipe U-bolt measures 2-1/2 in. internally. Pipe wall and schedule are in the Pipe Schedule Chart.

The inside width must accommodate the actual OD or width of the object, product-specific clearance, any coating or liner, and manufacturing tolerance. In a basic fit sense C must be at least the pipe OD, but do not invent a universal clearance value. Across the full Fastenal list, C minus OD ranges from 0.000 to 0.200 in. Manufacturer dimensions govern.

The inside length must be long enough for the object height or diameter, any saddle or mounting plate, washers, nuts, the required thread engagement and installation clearance. Do not use a universal rule such as pipe diameter plus a fixed number of inches. Check how the manufacturer defines L.

Distinguish the overall leg length, the threaded portion and the unthreaded tangent. The selected U-bolt must leave usable thread after every clamped component is assembled. Fastenal lists thread length as a reference value, for example 1-1/4 in. on most 3/8 in. rod pipe sizes and 2 in. on its 6 and 8 in. pipe U-bolts.

Common rod diameters and their UNC thread designations are below. These are common coarse threads, not a statement that every U-bolt of that diameter must use UNC. Rod diameter alone does not establish load capacity. For bolt diameters generally see the Bolt Diameter Chart.

Complete Fastenal UBOLT.Z Dimension List

Thread size is written as diameter-threads per inch, such as 3/8-16. UNC is the coarse series and UNF the fine series, each with a thread class. Fastenal’s U-bolt product standard specifies ASME B1.1 UNC and UNF Class 1A threads. Full tables are in the Thread Size Chart, the UNC Thread Chart and the UNF Thread Chart.

Round-bend U-bolts wrap pipe, tube and other round members. ASME B18.31.5 includes dimensional requirements for round-bend U-bolts. The bend radius and the inside width must fit the actual supported object.

Square U-bolts go around square tubing, rectangular members, frames and equipment parts. Selection must consider both the member’s width and its depth, and the corner radius matters.

Metric U-bolts are commonly written as the thread size, inside width and inside length, such as M10 × inside width × inside length, depending on the supplier. Convert inches to millimeters with:

U-bolts are made from low-carbon steel, higher-strength or alloy steel, stainless steel and application-specific materials. Fastenal’s zinc-plated U-bolt standard specifies ASTM A307 Grade A material and mechanical requirements. ASTM A307 Grade A has a 60 ksi minimum tensile strength and is intended for general applications. Do not describe every carbon-steel U-bolt as ASTM A307, and do not treat 60 ksi as the strength of every U-bolt.

Choose the finish for the exposure, moisture, corrosive environment, temperature and material compatibility. ASC offers plain, zinc-plated, hot-dip galvanized and stainless steel options depending on the product configuration.

Size does not equal load rating. Capacity depends on the rod diameter, the material specification, thread condition, bend geometry, installation, direction of loading, support configuration, temperature and the manufacturer’s design. ASC publishes normal and side load capacities for its engineered Fig. 137 pipe-support U-bolt instead of relying on rod diameter alone, and it provides a straight-line interaction check, Pn/Pna + Ps/Psa ≤ 1, for combined loads. Its side-load values assume the nuts are snug tight.

For engineering explanation only, stress is force divided by area:

where σ is stress, P is the applied axial force and A is the resisting area. Threaded fasteners usually use the thread tensile stress area, not the full rod area.

This is not a U-bolt load calculator. A U-bolt has two legs, a bend and a clamped object, and its capacity comes from the manufacturer’s design data.

Engineered pipe-support U-bolts are a different product class from general-purpose clamps. ASC’s Fig. 137 Standard U-Bolt is recommended for support or guiding of heavy loads and is supplied with a carbon steel U-bolt and four finished hex nuts. ASC’s product page lists 1/2 through 36 in. pipe sizes and its submittal lists 3/4 through 36 in. The product complies with MSS SP-58 (Type 24), MSS SP-69 and related federal specifications. It is ordered by pipe size and rod size, for example 6 in. × 5/8 in.

Load-rated support selection needs the applicable support data. For support spacing see the Pipe Support Spacing Chart.

For square and rectangular tubing, take the inside width from the member width, and the inside length from the member depth plus any mounting plate and hardware. Choose the rod diameter from the design requirements. Do not apply nominal pipe-size charts to non-round members.

Accessories change the length you need. Saddle plates, flat mounting plates, washers, hex nuts, double nuts where specified, and liners or coatings all add to the stack. ASC’s Fig. 137 standard configuration includes four finished hex nuts. Match nuts and washers using the Nut Size Chart and the Washer Size Chart.

1. Identify the object being clamped.
2. Determine its actual OD or member width.
3. Select the bend style.
4. Determine the required inside width.
5. Determine the required inside length.
6. Select the rod diameter from design and load requirements.
7. Select the thread series.
8. Verify the thread length.
9. Select the material and finish.
10. Check the manufacturer’s tolerances and load data.

The lookup covers only Fastenal product standard UBOLT.Z Rev. 07. Use it as an example, not as a universal sizing tool.

Pipe U-Bolt Example

Existing U-Bolt Replacement

Tighten the nuts evenly, keep the U-bolt aligned and avoid spreading the legs. Set the saddle or plate in the correct position, protect the pipe or its coating where needed, and follow the manufacturer’s torque instructions. There is no universal U-bolt torque chart, because torque depends on material, diameter, thread condition, finish, lubrication, nuts and application. For general fastener torque references see the Bolt Torque Chart, which is not a U-bolt rating.

Limitations

Pipe References

Threaded Hardware