Verified by Rachel Mayfield, Supply Chain Analyst - May 2026
Photo by Győző Mórocz on Pexels
Every dimension, torque value, and thread specification for the M42 metric bolt in one reference card. M42 Bolt Specifications M42 is one of the most common metric fastener sizes in UK engineering, used across heavy structural and high-load joints.
| Property |
Value |
Standard |
| Nominal diameter |
42.0 mm |
ISO 261 |
| Coarse pitch |
4.5 mm |
ISO 261 |
| Fine pitch |
3.0 mm |
ISO 261 |
| Tap drill (coarse, 75% engagement) |
37.5 mm |
ISO 2306 |
| Tap drill (fine) |
39.0 mm |
ISO 2306 |
| Clearance hole - close |
43.0 mm |
ISO 273 |
| Clearance hole - medium |
45.0 mm |
ISO 273 |
| Clearance hole - coarse |
48.0 mm |
ISO 273 |
| Hex head A/F (spanner size) |
65.0 mm |
ISO 4014 |
| Hex head height |
26.0 mm |
ISO 4014 |
| Socket head cap screw head dia |
63.0 mm |
ISO 4762 |
| Socket head hex key size |
32.0 mm |
ISO 4762 |
| Tensile stress area |
1121 mm^2 |
ISO 898-1 |
| Minimum tensile strength 8.8 |
800 MPa |
ISO 898-1 |
| Minimum tensile strength 10.9 |
1040 MPa |
ISO 898-1 |
| Proof load 8.8 |
650.2 kN |
ISO 898-1 |
| Proof load 10.9 |
930.4 kN |
ISO 898-1 |
| Torque dry, class 8.8 |
3870 Nm |
VDI 2230 |
| Torque dry, class 10.9 |
5545 Nm |
VDI 2230 |
| Torque dry, class 12.9 |
6475 Nm |
VDI 2230 |
M42 thread pitch
Standard M42 bolts use a 4.5 mm coarse pitch. Fine pitch M42 x 3.0 is used where vibration resistance matters or in thin-wall components. Coarse pitch is the default - if a drawing says M42 with no pitch specified, it means M42 x 4.5 coarse.
M42 tap drill size
For M42 x 4.5 coarse pitch with 75% thread engagement, drill 37.5 mm. For fine pitch, drill 39.0 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.
M42 clearance hole
For a clearance hole where the bolt passes through, use 43.0 mm (close fit), 45.0 mm (medium), or 48.0 mm (coarse) per ISO 273.
M42 torque values
Dry M42 property class 8.8: torque to 3870 Nm. Class 10.9: 5545 Nm. Class 12.9: 6475 Nm. These values target 90% proof load with K=0.20 dry thread friction. If threads are oiled or coated, reduce by 20-25%. For critical joints, always verify against the fastener manufacturer's datasheet.
M42 spanner and hex key
An M42 hex head bolt (ISO 4014) has 65.0 mm across flats, so you need a 65.0 mm spanner or socket. M42 socket head cap screws (ISO 4762) have 63.0 mm head diameter and need a 32.0 mm hex key (Allen key).
Related standards
- ISO 261 - ISO general-purpose metric screw threads
- ISO 273 - Fasteners: clearance holes for bolts and screws
- ISO 898-1 - Mechanical properties of carbon steel fasteners
- ISO 4014 - Hexagon head bolts, product grades A and B
- ISO 4762 - Hexagon socket head cap screws
- VDI 2230 - Systematic calculation of bolted joints
M42 bolts and tools on Amazon
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