Screw Thread & Tap Drill Chart
This chart gives 39 screw threads, Unified #0 to 1 in (UNC/UNF) and ISO metric M1 to M24, with major diameter in inches and millimetres, coarse and fine pitch, and the tap drill for each at roughly 75% thread engagement.
39 rows
| #0 | Unified | 0.0600 | 1.524 | — | — | 80 TPI | 3/64" (1.21 mm exact) |
| #1 | Unified | 0.0730 | 1.854 | 64 TPI | #53 (1.46 mm exact) | 72 TPI | #53 (1.50 mm exact) |
| #2 | Unified | 0.0860 | 2.184 | 56 TPI | #51 (1.73 mm exact) | 64 TPI | #50 (1.79 mm exact) |
| #3 | Unified | 0.0990 | 2.515 | 48 TPI | 5/64" (1.99 mm exact) | 56 TPI | #46 (2.06 mm exact) |
| #4 | Unified | 0.1120 | 2.845 | 40 TPI | #44 (2.21 mm exact) | 48 TPI | #43 (2.32 mm exact) |
| #5 | Unified | 0.1250 | 3.175 | 40 TPI | #39 (2.54 mm exact) | 44 TPI | #38 (2.60 mm exact) |
| #6 | Unified | 0.1380 | 3.505 | 32 TPI | #36 (2.71 mm exact) | 40 TPI | #33 (2.87 mm exact) |
| #8 | Unified | 0.1640 | 4.166 | 32 TPI | #29 (3.37 mm exact) | 36 TPI | #29 (3.46 mm exact) |
| #10 | Unified | 0.1900 | 4.826 | 24 TPI | #25 (3.77 mm exact) | 32 TPI | #21 (4.03 mm exact) |
| #12 | Unified | 0.2160 | 5.486 | 24 TPI | #17 (4.43 mm exact) | 28 TPI | #15 (4.58 mm exact) |
| 1/4" | Unified | 0.2500 | 6.350 | 20 TPI | #8 (5.08 mm exact) | 28 TPI | #3 (5.44 mm exact) |
| 5/16" | Unified | 0.3125 | 7.938 | 18 TPI | F (6.53 mm exact) | 24 TPI | I (6.88 mm exact) |
| 3/8" | Unified | 0.3750 | 9.525 | 16 TPI | 5/16" (7.94 mm exact) | 24 TPI | Q (8.47 mm exact) |
| 7/16" | Unified | 0.4375 | 11.113 | 14 TPI | U (9.30 mm exact) | 20 TPI | W (9.84 mm exact) |
| 1/2" | Unified | 0.5000 | 12.700 | 13 TPI | 27/64" (10.75 mm exact) | 20 TPI | 29/64" (11.43 mm exact) |
| 9/16" | Unified | 0.5625 | 14.287 | 12 TPI | 31/64" (12.17 mm exact) | 18 TPI | 1/2" (12.88 mm exact) |
| 5/8" | Unified | 0.6250 | 15.875 | 11 TPI | 17/32" (13.57 mm exact) | 18 TPI | 9/16" (14.46 mm exact) |
| 3/4" | Unified | 0.7500 | 19.050 | 10 TPI | 21/32" (16.51 mm exact) | 16 TPI | 11/16" (17.46 mm exact) |
| 7/8" | Unified | 0.8750 | 22.225 | 9 TPI | 49/64" (19.40 mm exact) | 14 TPI | 51/64" (20.41 mm exact) |
| 1" | Unified | 1.0000 | 25.400 | 8 TPI | 7/8" (22.23 mm exact) | 12 TPI | 59/64" (23.28 mm exact) |
| M1 | ISO metric | 0.0394 | 1.000 | 0.25 mm | 0.80 mm (0.75 mm exact) | 0.2 mm | 0.80 mm (0.80 mm exact) |
| M1.2 | ISO metric | 0.0472 | 1.200 | 0.25 mm | 1.00 mm (0.95 mm exact) | 0.2 mm | 1.00 mm (1.00 mm exact) |
| M1.4 | ISO metric | 0.0551 | 1.400 | 0.3 mm | 1.10 mm (1.10 mm exact) | 0.2 mm | 1.20 mm (1.20 mm exact) |
| M1.6 | ISO metric | 0.0630 | 1.600 | 0.35 mm | 1.20 mm (1.25 mm exact) | 0.2 mm | 1.40 mm (1.40 mm exact) |
| M1.8 | ISO metric | 0.0709 | 1.800 | 0.35 mm | 1.40 mm (1.45 mm exact) | 0.2 mm | 1.60 mm (1.60 mm exact) |
| M2 | ISO metric | 0.0787 | 2.000 | 0.4 mm | 1.60 mm (1.60 mm exact) | 0.25 mm | 1.80 mm (1.75 mm exact) |
| M2.5 | ISO metric | 0.0984 | 2.500 | 0.45 mm | 2.00 mm (2.05 mm exact) | 0.35 mm | 2.20 mm (2.15 mm exact) |
| M3 | ISO metric | 0.1181 | 3.000 | 0.5 mm | 2.50 mm (2.50 mm exact) | 0.35 mm | 2.60 mm (2.65 mm exact) |
| M3.5 | ISO metric | 0.1378 | 3.500 | 0.6 mm | 2.90 mm (2.90 mm exact) | 0.35 mm | 3.20 mm (3.15 mm exact) |
| M4 | ISO metric | 0.1575 | 4.000 | 0.7 mm | 3.30 mm (3.30 mm exact) | 0.5 mm | 3.50 mm (3.50 mm exact) |
| M5 | ISO metric | 0.1968 | 5.000 | 0.8 mm | 4.20 mm (4.20 mm exact) | 0.5 mm | 4.50 mm (4.50 mm exact) |
| M6 | ISO metric | 0.2362 | 6.000 | 1 mm | 5.00 mm (5.00 mm exact) | 0.75 mm | 5.20 mm (5.25 mm exact) |
| M8 | ISO metric | 0.3150 | 8.000 | 1.25 mm | 6.80 mm (6.75 mm exact) | 1 mm | 7.00 mm (7.00 mm exact) |
| M10 | ISO metric | 0.3937 | 10.000 | 1.5 mm | 8.50 mm (8.50 mm exact) | 1.25 mm | 8.80 mm (8.75 mm exact) |
| M12 | ISO metric | 0.4724 | 12.000 | 1.75 mm | 10.20 mm (10.25 mm exact) | 1.5 mm | 10.50 mm (10.50 mm exact) |
| M14 | ISO metric | 0.5512 | 14.000 | 2 mm | 12.00 mm (12.00 mm exact) | 1.5 mm | 12.50 mm (12.50 mm exact) |
| M16 | ISO metric | 0.6299 | 16.000 | 2 mm | 14.00 mm (14.00 mm exact) | 1.5 mm | 14.50 mm (14.50 mm exact) |
| M20 | ISO metric | 0.7874 | 20.000 | 2.5 mm | 17.50 mm (17.50 mm exact) | 1.5 mm | 18.50 mm (18.50 mm exact) |
| M24 | ISO metric | 0.9449 | 24.000 | 3 mm | 21.00 mm (21.00 mm exact) | 2 mm | 22.00 mm (22.00 mm exact) |
Source: Unified threads per ASME B1.1 (UNC/UNF); metric per ISO 262 selected sizes. Numbered-screw major diameters follow D = 0.060 + 0.013 N inches exactly.
Notes
Tap drill is the roughly 75% engagement rule — major diameter less 1/TPI for unified threads, less the pitch for metric — with the nearest stocked drill in brackets. Published preferred-tap charts round by convention rather than by formula and may differ by one size; for metric threads the rule is the convention and the two agree.
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