M4 thread sizes
3.3 mm tapping drill · 4.5 mm clearance
0.7 mm coarse pitch · 3 mm hex key · 7 mm spanner
What M4 is used for
Light brackets, panel fixings and small machine assemblies.
Every number for M4
| Major diameter | 4 mm |
| Coarse pitch | 0.7 mm |
| Tapping drill, coarse | 3.3 mm (4 − 0.7 = 3.3) |
| Clearance hole, normal | 4.5 mm |
| Hex key (socket head) | 3 mm |
| Spanner (hex head) | 7 mm |
| Tapped depth, steel | 6.0 mm (1.5 × diameter) |
| Tapped depth, aluminium | 8.0 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 M4 coarse that is 4 − 0.7 = 3.3 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 | 0.4 mm | 1.6 mm | 2.4 mm | 1.5 mm |
| 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 |
| M5 | 0.8 mm | 4.2 mm | 5.5 mm | 4 mm |
| M6 | 1 mm | 5 mm | 6.6 mm | 5 mm |
Frequently asked questions
What drill size for M4?
3.3 mm for a coarse thread. The rule is major diameter minus pitch: 4 − 0.7 = 3.3.
What is the clearance hole for M4?
4.5 mm for a normal fit under ISO 273. A close fit is about 4.3 mm and a loose fit around 4.9 mm — the clearance hole is the one in the part the bolt passes through, not the one being tapped.
What size spanner for an M4 bolt?
7 mm across the flats for a standard hex head. A socket head cap screw of the same size takes a 3 mm hex key instead.
What is the pitch of M4?
0.7 mm coarse. Pitch is the distance between adjacent thread crests, so one full turn advances the bolt 0.7 mm.