Screw Size Chart
Screw sizes are identified by gauge number, with higher numbers indicating larger diameters. The chart below covers the most common wood and machine screw sizes from #2 through #14, including diameter measurements, thread counts for both coarse and fine threads, and the recommended pilot hole size for each gauge.
| Gauge | Diameter (in) | Diameter (mm) | TPI Coarse | TPI Fine | Pilot Hole | Common Use |
|---|---|---|---|---|---|---|
| #2 | 0.086" | 2.18 mm | 56 | 64 | 1/16" (1.6 mm) | Hinges, small hardware |
| #3 | 0.099" | 2.51 mm | 48 | 56 | 5/64" (2 mm) | Light-duty fastening |
| #4 | 0.112" | 2.84 mm | 40 | 48 | 5/64" (2 mm) | Electrical covers, light fixtures |
| #5 | 0.125" | 3.18 mm | 40 | 44 | 3/32" (2.4 mm) | Cabinet hardware |
| #6 | 0.138" | 3.51 mm | 32 | 40 | 7/64" (2.8 mm) | General woodworking, trim |
| #7 | 0.151" | 3.84 mm | 32 | 36 | 7/64" (2.8 mm) | Medium-duty wood projects |
| #8 | 0.164" | 4.17 mm | 32 | 36 | 1/8" (3.2 mm) | Most common screw size, general purpose |
| #9 | 0.177" | 4.50 mm | 24 | 32 | 9/64" (3.6 mm) | Decking, outdoor projects |
| #10 | 0.190" | 4.83 mm | 24 | 32 | 9/64" (3.6 mm) | Structural wood connections, shelving |
| #12 | 0.216" | 5.49 mm | 24 | 28 | 11/64" (4.4 mm) | Heavy-duty fastening, framing |
| #14 | 0.242" | 6.15 mm | 20 | 24 | 13/64" (5.2 mm) | Heavy structural work, lag applications |
Screw Sizing Tips
Understanding Gauge Numbers
Screw gauge numbers correspond to the major diameter of the screw shaft. Each gauge increase adds 0.013 inches to the diameter, starting from a base of 0.060 inches for a #0 screw. The formula is: diameter = 0.060 + (gauge x 0.013). For example, a #8 screw has a diameter of 0.060 + (8 x 0.013) = 0.164 inches.
Coarse vs Fine Threads
Coarse threads (UNC) are the default for most applications. They are easier to start, more forgiving of cross-threading, and work better in softer materials like wood and plastic. Fine threads (UNF) provide stronger clamping force and are preferred for metal-to-metal connections, vibration-prone assemblies, and applications requiring precise adjustment.
Pilot Hole Sizing
The pilot hole sizes listed above are for hardwood. For softwood like pine or cedar, you can often use a pilot hole one size smaller, or skip the pilot hole entirely for screws #8 and smaller. Always drill a pilot hole in hardwood to prevent splitting.