A designation such as #10-16 × 3/4 is a nominal #10 screw (0.190 in. diameter), 16 threads per inch, and 3/4 in. nominal length. It does not mean 10-gauge sheet metal, 16-gauge sheet metal, a 10/16 in. diameter or a 16 mm length.

Not every diameter, thread, head and point exists in every length. Length conventions also vary by head style, as shown in the diagram above.

A screw number is a size label, not a fraction. A #6 screw is 0.138 in., not 6/64 in. (0.094 in.), and a #8 screw is 0.164 in., not 1/8 in. (0.125 in.). Use the nominal diameter column in the chart. For the numbered series, the diameter follows D = 0.060 + 0.013N, where N is the screw number.

The formula applies to the numbered series only. Do not extend it into fractional sizes such as 1/4 in. For machine-screw and wood-screw numbering, see the machine screw size chart.

Screw gauge is a fastener diameter designation. Sheet-metal gauge is a material-thickness designation, and the thickness for a given gauge depends on the material (steel, galvanized steel, aluminum) and the gauge standard. The two numbers have no connection. To look up actual thickness, use the sheet metal gauge chart.

#4 and #6 screws are small, light-duty sizes. Thread style and point type still matter, and no universal sheet-thickness capacity applies to either size. Check the manufacturer’s data for the specific screw. For drywall-to-steel attachment, a different screw family applies; see drywall screw spacing.

A #8 screw has a nominal ASME diameter of 0.164 in. (4.2 mm). Self-drilling #8 screws are real product families: for example, a #8-18 × 1/2 hex washer head screw with a #2 drill point is listed by Hilti with a drilling capacity of 0.035 to 0.100 in. and by Buildex at 0.036 to 0.100 in. Those are product-specific values for that screw, not a rule for every #8 screw.

A #10 screw is 0.190 in. (4.8 mm) nominal. The common designation is #10-16 (16 threads per inch), but other thread configurations exist. The same #10-16 size also shows how point style changes capacity: in Hilti’s technical guide, an S-MD 10-16 × 3/4 screw with a #2 point lists 0.035 to 0.110 in. drilling capacity, while the same size with a #3 point lists 0.110 to 0.175 in. Same diameter, same thread, different points.

A #12 screw has a nominal ASME diameter of 0.216 in. (5.5 mm). Some manufacturers list a slightly different measured product diameter, such as 0.210 in. for certain Buildex #12 screws, so always confirm the product data. Common self-drilling designations are #12-14 and #12-24, and they should not be treated as equal in drilling capacity: the #12-14 TEKS 2 lists 0.036 to 0.210 in., while a #12-24 TEKS 5 lists 0.125 to 0.500 in.

A fractional 1/4 in. screw is 0.250 in. nominal. The numbered-series formula would give 0.242 in. for #14 (0.060 + 0.013 × 14), but sheet-metal and self-drilling screws in this size range are normally sold as 1/4 in. screws, such as 1/4-14 Type AB or 1/4-28 TEKS 5. Do not casually treat every manufacturer’s “#14” and every 1/4 in. fastener as identical; check the governing product standard and the actual diameter on the data sheet.

A #10-16 screw has a pitch of 1/16 = 0.0625 in., and a #12-24 screw has a pitch of 1/24 = 0.04167 in. Pitch is not sheet thickness, and TPI is not metal gauge. For fine and coarse thread standards in general, see the thread size chart.

Self-tapping screws form or cut their own mating thread as they enter the material, but some require a predrilled hole. Self-drilling screws have an integrated drill point that drills the hole before the threads engage. SAE J78 describes the goal of self-drilling tapping screws as drilling a hole and then forming or cutting mating threads without deforming their own thread and without breaking during assembly.

The ASME tapping-screw standard (B18.6.3) has separate dimensional provisions for several thread and point styles. Do not assume every Type A or AB screw uses the same pilot hole: it depends on the exact thread form, screw size, substrate material, material thickness and the manufacturer’s specification.

SAE J78 covers carbon steel self-drilling tapping screws with point Styles 2, 3, 4 and 5. A drill-point number is not the screw diameter: a #12 screw can be made with several different drill points. Buildex also notes that drill and tap capacities may vary with special feature designs, so refer to the product report for the exact part.

Compare three #12 examples from Buildex. A #12-14 TEKS 2 lists 0.036 to 0.210 in. A #12-24 TEKS 4.5 lists 0.125 to 0.375 in. A #12-24 TEKS 5 lists 0.125 to 0.500 in. The nominal size is the same family, but the drilling capacity is very different, and the thread count also changes between them.

A #12-14 TEKS 3 shows the same 0.036 to 0.210 in. range as the TEKS 2 in Buildex listings, so the point number alone does not tell you the range. Always read the data for the exact part number.

The hole size in the table is tied to the test sheet thickness in the last column. In thinner sheet a smaller pilot is generally used to maintain thread engagement, while thicker or harder material may need a slightly larger one. Self-tapping screws may need a pilot hole, while self-drilling screws do not need a separate one within rated drilling capacity. For drill designations (number, letter and fractional), see the drill bit size chart and the pilot hole size page.

Thin sheet leans on point and thread engagement: the screw must grip the metal without stripping it. As steel gets thicker, the drill-point capacity becomes increasingly important, because the point must be able to drill through the entire stack before the threads start. Use the sheet metal thickness page for the actual thickness of a given gauge, and add up the total thickness of every layer being drilled.

Manufacturers publish thickness limits per product. For example, Hilti lists an S-MD 8-18 × 1/2 screw at 0.035 to 0.100 in. drilling capacity with a maximum total thickness of 1/8 in., and a #10-16 × 3/4 screw with a #3 point at 0.110 to 0.175 in. Those are product-specific limits.

A table like “22 gauge = #8, 18 gauge = #10, 14 gauge = #12” looks helpful but would be misleading. Screw suitability depends on all of the following:

• Screw diameter and thread pitch
• Point style and drill-point length
• Steel thickness and number of layers
• Attachment thickness and substrate thickness
• Steel strength and connection type
• Required pullout, pullover and shear strength
• Manufacturer or evaluation-report limitations

Common nominal screw lengths include 1/2, 5/8, 3/4, 1-1/4, 1-1/2 and 2 in., with longer sizes available in some product lines. Not every diameter, head style and point type exists in every length.

Every row has the same drilling capacity. Longer screws allow a thicker stack of material, but they do not drill thicker steel. Screw length does not equal drill capacity, and diameter does not equal drill capacity: the point design is critical. A #12 TEKS 2 × 2 in. screw may be longer than a #12 TEKS 5 × 1-1/4 in. screw, yet the TEKS 5 point can have the greater drilling capacity.

How many threads should extend through the metal depends on the product and its evaluation. Buildex states that its TEKS fasteners must penetrate beyond the metal structure a minimum of three pitches of thread. Treat that as an example for that product, not as a universal “always leave three threads showing” rule for every sheet-metal screw.

The drill point must also clear the back of the substrate before the threads engage, so a screw that only just reaches through the steel can fail to form proper threads. Follow the product data and, for structural connections, the evaluation report.

Common styles are hex washer, pan, flat (countersunk), oval and pancake (low-profile) heads. A larger head or washer bears on more sheet, which affects pullover behavior, so the head style matters as much as the screw diameter. For a visual guide to head shapes, see the screw head types, and for washers see the washer size chart.

The same #12-24 TEKS 5 screw appears with a 5/16 in. hex washer head in one length and a 3/8 in. hex washer head in another, so head style and product family can change the required driver. Hex socket, Phillips and square or combination drives are all used. Do not infer a driver size from screw gauge alone.

• Tensile strength: the fastener itself pulling apart.
• Shear strength: the fastener cross-section being cut across.
• Pullout: thread engagement being pulled out of the substrate.
• Pullover: the sheet beneath the screw head or washer tearing around the head.

The table shows why bigger is not automatically stronger: pullout climbs with steel thickness, while pullover levels off once the head size becomes the limit. Connection strength can also be controlled by sheet tearing, edge distance, spacing and steel grade.

Steel-to-steel connections depend on substrate thickness, attachment thickness, drill point, thread engagement and an evaluated connection. ICC-ES ESR-1976 evaluates ITW Buildex TEKS self-drilling fasteners for engineered or code-prescribed connections of cold-formed steel framing and of sheet steel sheathing to cold-formed steel framing. It tabulates drilling capacity and minimum protrusion for the products it covers. Check ICC-ES for the current active revision of the report.

When a screw is not a good fit for a thin connection, rivets are one alternative; see the rivet size chart.

Aluminum

Do not carry steel connection data over to aluminum automatically. ICC-ES AC491 sets evaluation provisions for self-drilling tapping screws used with aluminum because of aluminum’s distinct mechanical behavior. It covers aluminum-to-aluminum, aluminum-to-steel and steel-to-aluminum connections, and screws of carbon steel, stainless steel and bi-metal construction in specific sizes.

Stainless Steel

Stainless screws offer corrosion resistance, but do not assume they have the same drilling or structural capacity as carbon-steel products. Check galvanic compatibility with the metals being joined and the exposure. Hilti also warns that many hardened steel fasteners are not recommended with dissimilar metals or chemically treated wood where moisture or corrosion is present, because of the risk of delayed hydrogen-assisted stress corrosion cracking.

Exterior and Roofing

Exterior screws need corrosion-resistant coatings, sealing washers where water-tightness matters, and an appropriate head. Follow the roofing or panel manufacturer’s fastening requirements. This page does not cover roof-screw spacing.

1. Use the correct driver or socket for the head.
2. Use a screwgun with a depth-sensitive nosepiece within the product’s recommended speed range (Buildex lists 0 to 2,000 or 0 to 2,500 RPM depending on the product, with a maximum of 1,800 RPM for TEKS 5).
3. Drive perpendicular to the surface.
4. Seat the fastener fully; Buildex says it is fully seated when the head is flush with the work surface.
5. Do not overdrive: Buildex warns that overdriving can cause torsional failure of the fastener or stripout of the substrate.
6. Confirm the fastener extends beyond the metal by the required thread protrusion (three pitches for TEKS).

These instructions come from Buildex product literature and apply to its Teks products. Follow the instructions for the fastener you actually use.

Standards and References Used

Manufacturer values are specific to the exact product, head style, coating and steel properties listed. Local codes, project specifications and the engineer of record govern structural connections.