Reference & Charts
Socket Head Cap Screw Dimensions
Standard head diameter, head height, and hex key size for inch (ASME B18.3) and metric (ISO 4762) socket head cap screws — the numbers you need to size counterbores and clearance holes.
Last verified: 2026-07-09
Socket head cap screws (SHCS) have a cylindrical head driven by a hex (Allen) key. These are the standard head dimensions — use the head diameter and height to size a counterbore so the head seats below flush, and the hex key column to grab the right driver.
Inch — ASME B18.3
| Size | Nominal Ø | Head Ø | Head height | Hex key |
|---|---|---|---|---|
| #4-40 | 0.112 | 0.183 | 0.112 | 3/32 |
| #6-32 | 0.138 | 0.226 | 0.138 | 7/64 |
| #8-32 | 0.164 | 0.27 | 0.164 | 9/64 |
| #10-24 | 0.19 | 0.312 | 0.19 | 5/32 |
| 1/4-20 | 0.25 | 0.375 | 0.25 | 3/16 |
| 5/16-18 | 0.3125 | 0.469 | 0.3125 | 1/4 |
| 3/8-16 | 0.375 | 0.562 | 0.375 | 5/16 |
| 1/2-13 | 0.5 | 0.75 | 0.5 | 3/8 |
| 5/8-11 | 0.625 | 0.938 | 0.625 | 1/2 |
| 3/4-10 | 0.75 | 1.125 | 0.75 | 5/8 |
Metric — ISO 4762
| Size | Nominal Ø | Head Ø | Head height | Hex key |
|---|---|---|---|---|
| M3 | 3 | 5.5 | 3 | 2.5 |
| M4 | 4 | 7 | 4 | 3 |
| M5 | 5 | 8.5 | 5 | 4 |
| M6 | 6 | 10 | 6 | 5 |
| M8 | 8 | 13 | 8 | 6 |
| M10 | 10 | 16 | 10 | 8 |
| M12 | 12 | 18 | 12 | 10 |
| M16 | 16 | 24 | 16 | 14 |
| M20 | 20 | 30 | 20 | 17 |
Frequently asked
- How deep should the counterbore be?
- At least the head height, plus a little so the head sits below flush. For an M6 (6 mm head height), a counterbore ~6.5 mm deep leaves the head just below the surface. The Counterbore Calculator does this from these dimensions.
- What hex key fits an M6 socket head cap screw?
- A 5 mm hex (Allen) key. See the hex key column for each size.
Sources
- ASME B18.3 — Socket Cap, Shoulder, and Set Screws (inch)
- ISO 4762 — Hexagon socket head cap screws (metric)