Metric
(ISO 4762) The "Allen bolt." It has a deep internal hex drive. It allows for high torque and is used when space is too tight for a wrench.
| Thread Designation | Head Diameter (mm) | Head Height (mm) | Clearance Hole (mm) | Thread Pitch (mm) |
|---|---|---|---|---|
| M1.6 | 3.0 | 1.6 | 1.8 | 0.35 |
| M2 | 3.8 | 2.0 | 2.4 | 0.40 |
| M2.5 | 4.5 | 2.5 | 2.9 | 0.45 |
| M3 | 5.5 | 3.0 | 3.4 | 0.50 |
| M4 | 7.0 | 4.0 | 4.5 | 0.70 |
| M5 | 8.5 | 5.0 | 5.5 | 0.80 |
| M6 | 10.0 | 6.0 | 6.6 | 1.00 |
| M8 | 13.0 | 8.0 | 9.0 | 1.25 |
| M10 | 16.0 | 10.0 | 11.0 | 1.50 |
| M12 | 18.0 | 12.0 | 13.5 | 1.75 |
| M16 | 24.0 | 16.0 | 17.5 | 2.00 |
| M20 | 30.0 | 20.0 | 22.0 | 2.50 |
| M24 | 36.0 | 24.0 | 26.0 | 3.00 |
Imperial
For Socket Head Cap Screws (SHCS) in Imperial sizes, the standard is ASME B18.3.
| Thread Designation | Head Diameter (in) | Head Height (in) | Clearance Hole (in) | Threads Per Inch (TPI) |
|---|---|---|---|---|
| #0-80 | 0.096" | 0.060" | 0.063" | 80 |
| #2-56 | 0.140" | 0.086" | 0.089" | 56 |
| #4-40 | 0.183" | 0.112" | 0.116" | 40 |
| #6-32 | 0.226" | 0.138" | 0.144" | 32 |
| #8-32 | 0.270" | 0.164" | 0.169" | 32 |
| #10-24 | 0.312" | 0.190" | 0.196" | 24 |
| 1/4"-20 | 0.375" | 0.250" | 17/64" | 20 |
| 5/16"-18 | 0.469" | 0.312" | 21/64" | 18 |
| 3/8"-16 | 0.562" | 0.375" | 25/64" | 16 |
| 7/16"-14 | 0.656" | 0.438" | 29/64" | 14 |
| 1/2"-13 | 0.750" | 0.500" | 17/32" | 13 |
| 5/8"-11 | 0.938" | 0.625" | 21/32" | 11 |
| 3/4"-10 | 1.125" | 0.750" | 25/32" | 10 |