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M3 bolt size
5.5 mm wrench
across-flats spanner / socket size for M3
M3 bolt — electronics, 3D printers and small brackets.
Full specification
| System | Metric coarse |
| Nominal diameter | 3 mm |
| Thread pitch | 0.5 mm |
| Wrench / spanner (across flats) | 5.5 mm |
| Tap drill | 2.5 mm |
| Clearance hole | 3.4 mm |
| Common grade / class | 8.8 |
| Typical torque | 1.3 Nm (1 ft·lb) |
| Closest other-system size | ~#5 imperial |
🔧 Torque unit converter
Pre-filled with the typical torque for M3 (8.8, dry). Edit any field to convert.
⚠️ Torque values here are general references for 8.8 on clean, dry threads. Lubrication, coatings, and the joint material change the figure significantly. For structural, automotive, or safety-critical work, always use the torque specified by the manufacturer or engineer.
About M3
M3 is the workhorse of electronics and 3D printing, used for almost every small assembly.
For 3D-printed parts, use heat-set M3 inserts rather than threading directly into plastic.
Frequently asked questions
- What size wrench or spanner fits M3?
- M3 bolt uses a 5.5 mm wrench or spanner, measured across the flats of the hex head.
- What is the torque for M3?
- A typical tightening torque for M3 bolt in 8.8 on dry threads is about 1.3 Nm (1 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does M3 use?
- M3 bolt has a thread pitch of 0.5 mm and uses a 2.5 mm tap drill, with a 3.4 mm clearance hole.