Metric Fastener Bolt Geometry Dimensions Table
Dimensional envelope sizes for standard ISO metric fasteners including thread pitch, head flats, and height.
Overview & Scope
Standard metric fastener dimensions, ISO 898-1 property classes, proof loads, and wrench socket envelopes per ISO 4014, ISO 4017, ISO 898-1, and ASME B18.2.1. Tensile stress area ($A_s$) governs structural joint clamp force, tightening torque, and yield utilization limits.
Technical Sizing Values
The table below specifies thread pitch, nominal tensile stress area ($A_s$), hexagon head width across flats ($s$), head height ($k$), socket clearance envelope, and proof load ratings ($F_p$) for Property Classes 8.8 and 10.9 across metric sizes M3 through M64.
| Thread Size | Thread Pitch (mm) | Tensile Area (mm²) | Width Across Flats (mm) | Head Height (mm) | Flats Clearances (mm) | Proof Load 8.8 (kN) | Proof Load 10.9 (kN) |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 5.03 | 5.5 | 2 | 6.4 | 3.02 | 4.17 |
| M4 | 0.7 | 8.78 | 7 | 2.8 | 8.1 | 5.27 | 7.29 |
| M5 | 0.8 | 14.2 | 8 | 3.5 | 9.2 | 8.52 | 11.79 |
| M6 | 1 | 20.1 | 10 | 4 | 11.5 | 12.06 | 16.68 |
| M8 | 1.25 | 36.6 | 13 | 5.3 | 15 | 21.96 | 30.38 |
| M10 | 1.5 | 58 | 16 | 6.4 | 18.4 | 34.8 | 48.14 |
| M12 | 1.75 | 84.3 | 18 | 7.5 | 20.8 | 50.58 | 69.97 |
| M16 | 2 | 157 | 24 | 10 | 27.7 | 94.2 | 130.31 |
| M20 | 2.5 | 245 | 30 | 12.5 | 34.6 | 159.25 | 203.35 |
| M24 | 3 | 353 | 36 | 15 | 41.6 | 229.45 | 292.99 |
| M27 | 3 | 459 | 41 | 17 | 47.3 | 298.35 | 380.97 |
| M30 | 3.5 | 561 | 46 | 18.7 | 53.1 | 364.65 | 465.63 |
| M36 | 4 | 817 | 55 | 22.5 | 63.5 | 531.05 | 678.11 |
| M42 | 4.5 | 1121 | 65 | 26 | 75 | 728.65 | 930.43 |
| M48 | 5 | 1473 | 75 | 30 | 86.5 | 957.45 | 1222.59 |
| M56 | 5.5 | 2030 | 85 | 35 | 98 | 1319.5 | 1684.9 |
| M64 | 6 | 2676 | 95 | 40 | 110 | 1739.4 | 2221.08 |
Engineering Notes & Best Practices
- •Tensile stress area ($A_s$) is calculated per ISO 898-1 as $A_s = \frac{\pi}{4}(d - 0.9382 P)^2$, accounting for the root diameter reduction from 60° triangular thread geometry.
- •Proof load ($F_p$) represents the elastic threshold force ($F_p = S_p \times A_s$) up to which zero plastic elongation occurs after 15 seconds of sustained axial tension.
- •Width across flats ($s$) determines the required open-end wrench, box wrench, or socket size; flats clearance defines the minimum spatial envelope required to fit standard industrial sockets during machine assembly.
- •For dynamic cyclic loading, tightening preload is recommended at 75% to 90% of proof load ($F_i = 0.75\text{ to }0.90 \times F_p$) to prevent bolt fatigue and joint separation.
- •Cross-reference bolt clamp loads and friction coefficients with our [Bolt Preload & Tightening Torque PRO Suite](/calculators/bolt-torque) and [ISO 898-1 Fastener Mechanical Properties Reference](/standards/iso-898-1-fastener-grades).
Dataset Citations & References
ISO 4014 / ISO 4017 Specifications
Public domain source and standard catalog reference parameters.
Machinery's Handbook
Public domain source and standard catalog reference parameters.