Hex Bolt Spec Table
Across-flats (AF) reference for standard ISO 4014 (KS B 1002 / DIN 933) hex bolts from M3 to M48. AF is the dimension that determines spanner, box, and socket sizes. Grade 8.8 dry tightening torque is included so engineers can select a wrench and verify clamp force at a glance on the shop floor. Some legacy Japanese JIS equipment uses a different AF series — verify with calipers when mixing old and new parts.
Practical Notes
- Bolt length: nut height + washer thickness + clamped material + 2–3 extra pitches. Bolt end must extend at least 1.5 pitches below nut for proper clamping.
- Strength mismatch: using class 4 nuts with grade 10.9 bolts causes nut thread failure first. Always verify bolt-nut strength grade compatibility.
- Zinc-plated bolts risk hydrogen embrittlement above 200°C. For high-temperature environments, select products with post-heat-treatment hydrogen de-embrittlement (baking).
Selection Guide
Use for general external fastening where wrench access is available. Hex heads transmit higher torque than socket heads but protrude above the surface. Most economical in M6–M24 range; grade 8.8 suffices for most mechanical joints. Consider socket bolts for flush mounting, flat-head bolts for aesthetics. In high-vibration environments, use flange bolts or lock nuts.
Hex Bolt
KSISOJISDINHex Bolt
16 sizesThe dimensions below are identical across KS B 1002 · ISO 4014 · JIS B 1180 · DIN 931.
Width across flats B follows DIN 931. ISO 4014 differs at M10, M12, M14 and M22 (16, 18, 21, 34).
| Nominal | d | P | H (Head H.) | B (Wrench) | C (Corner) |
|---|---|---|---|---|---|
| M6 | 6 | 1 | 4 | 10 | 11.5 |
| M8 | 8 | 1.25 | 5.5 | 13 | 15 |
| M10 | 10 | 1.5 | 7 | 17 | 19.6 |
| M12 | 12 | 1.75 | 8 | 19 | 21.9 |
| M14 | 14 | 2 | 9 | 22 | 25.4 |
| M16 | 16 | 2 | 10 | 24 | 27.7 |
| M18 | 18 | 2.5 | 12 | 27 | 31.2 |
| M20 | 20 | 2.5 | 13 | 30 | 34.6 |
| M22 | 22 | 2.5 | 14 | 32 | 37 |
| M24 | 24 | 3 | 15 | 36 | 41.6 |
| M27 | 27 | 3 | 17 | 41 | 47.3 |
| M30 | 30 | 3.5 | 19 | 46 | 53.1 |
| M33 | 33 | 3.5 | 21 | 50 | 57.7 |
| M36 | 36 | 4 | 23 | 55 | 63.5 |
| M42 | 42 | 4.5 | 26 | 65 | 75 |
| M48 | 48 | 5 | 30 | 75 | 86.5 |
Key Features
- Strength grades 4.8–12.9 available; high-temp grades (A2-70/A4-80) separate
- Wide size range M3–M64 with partial/full thread options
- KS B 1002 / ISO 4014 / DIN 931 compatible; wrench and socket interchangeable
Key Applications
Steel structures, machine frames, flange joints, automotive chassis, equipment anchoring
STEP File Downloads
Free 3D CAD models (STEP AP214). Built to real standard dimensions; threads are simplified (plain shank) per free-library convention.
FAQ
What are the head height (H) and across-flats (S) of a hex bolt?
For M10: head height ~7mm, across-flats (wrench size) 17mm. Refer to spec tables for exact dimensions per size.
Difference between partial-thread and full-thread bolts?
Partial-thread bolts have an unthreaded shank that resists shear loads on a solid cross-section. Full-thread bolts offer flexible clamping length but lower shear strength.