M2 thread sizes
1.6 mm tapping drill · 2.4 mm clearance
0.4 mm coarse pitch · 1.5 mm hex key · 4 mm spanner
What M2 is used for
Electronics, small hinges and instrument work.
Every number for M2
| Major diameter | 2 mm |
| Coarse pitch | 0.4 mm |
| Tapping drill, coarse | 1.6 mm (2 − 0.4 = 1.6) |
| Clearance hole, normal | 2.4 mm |
| Hex key (socket head) | 1.5 mm |
| Spanner (hex head) | 4 mm |
| Tapped depth, steel | 3.0 mm (1.5 × diameter) |
| Tapped depth, aluminium | 4.0 mm (2 × diameter) |
Where the drill size comes from
A tapping drill leaves enough material for the tap to cut a thread, and the amount it has to leave is one pitch: drill = major diameter − pitch. For M2 coarse that is 2 − 0.4 = 1.6 mm. The rule holds for the fine series too — subtract whichever pitch you are cutting.
Going slightly larger gives a shallower thread that is easier to tap and weaker; going smaller risks breaking the tap. The standard drill aims at about 75% thread engagement, which is where the strength stops improving enough to be worth the extra effort.
Nearby sizes
| Thread | Pitch | Tapping drill | Clearance | Hex key |
|---|---|---|---|---|
| M2.5 | 0.45 mm | 2.05 mm | 2.9 mm | 2 mm |
| M3 | 0.5 mm | 2.5 mm | 3.4 mm | 2.5 mm |
| M4 | 0.7 mm | 3.3 mm | 4.5 mm | 3 mm |
| M5 | 0.8 mm | 4.2 mm | 5.5 mm | 4 mm |
Frequently asked questions
What drill size for M2?
1.6 mm for a coarse thread. The rule is major diameter minus pitch: 2 − 0.4 = 1.6.
What is the clearance hole for M2?
2.4 mm for a normal fit under ISO 273. A close fit is about 2.2 mm and a loose fit around 2.8 mm — the clearance hole is the one in the part the bolt passes through, not the one being tapped.
What size spanner for an M2 bolt?
4 mm across the flats for a standard hex head. A socket head cap screw of the same size takes a 1.5 mm hex key instead.
What is the pitch of M2?
0.4 mm coarse. Pitch is the distance between adjacent thread crests, so one full turn advances the bolt 0.4 mm.