Verified by Rachel Mayfield, Supply Chain Analyst - May 2026
Photo by Győző Mórocz on Pexels
Every dimension, torque value, and thread specification for the M3 metric bolt in one reference card. M3 Bolt Specifications M3 is one of the most common metric fastener sizes in UK engineering, used across small panel mounting and instrumentation.
| Property |
Value |
Standard |
| Nominal diameter |
3.0 mm |
ISO 261 |
| Coarse pitch |
0.5 mm |
ISO 261 |
| Fine pitch |
0.35 mm |
ISO 261 |
| Tap drill (coarse, 75% engagement) |
2.5 mm |
ISO 2306 |
| Tap drill (fine) |
2.65 mm |
ISO 2306 |
| Clearance hole - close |
3.2 mm |
ISO 273 |
| Clearance hole - medium |
3.4 mm |
ISO 273 |
| Clearance hole - coarse |
3.6 mm |
ISO 273 |
| Hex head A/F (spanner size) |
5.5 mm |
ISO 4014 |
| Hex head height |
2.0 mm |
ISO 4014 |
| Socket head cap screw head dia |
5.5 mm |
ISO 4762 |
| Socket head hex key size |
2.5 mm |
ISO 4762 |
| Tensile stress area |
5.03 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 |
2.9 kN |
ISO 898-1 |
| Proof load 10.9 |
4.2 kN |
ISO 898-1 |
| Torque dry, class 8.8 |
1.3 Nm |
VDI 2230 |
| Torque dry, class 10.9 |
1.8 Nm |
VDI 2230 |
| Torque dry, class 12.9 |
2.1 Nm |
VDI 2230 |
M3 thread pitch
Standard M3 bolts use a 0.5 mm coarse pitch. Fine pitch M3 x 0.35 is used where vibration resistance matters or in thin-wall components. Coarse pitch is the default - if a drawing says M3 with no pitch specified, it means M3 x 0.5 coarse.
M3 tap drill size
For M3 x 0.5 coarse pitch with 75% thread engagement, drill 2.5 mm. For fine pitch, drill 2.65 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.
M3 clearance hole
For a clearance hole where the bolt passes through, use 3.2 mm (close fit), 3.4 mm (medium), or 3.6 mm (coarse) per ISO 273.
M3 torque values
Dry M3 property class 8.8: torque to 1.3 Nm. Class 10.9: 1.8 Nm. Class 12.9: 2.1 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.
M3 spanner and hex key
An M3 hex head bolt (ISO 4014) has 5.5 mm across flats, so you need a 5.5 mm spanner or socket. M3 socket head cap screws (ISO 4762) have 5.5 mm head diameter and need a 2.5 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
M3 bolts and tools on Amazon
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Looking for machine screw head sizes rather than bolt data? The M3 screw dimensions card covers pan, countersunk, socket cap, button and cheese heads with drive sizes and DIN vs ISO differences.