M3 Screw Hole Size
The right hole size for an M3 screw depends on one question: should the screw pass through the part (a clearance hole) or thread into it (a tapped hole)? The short answer: 3.2–3.6 mm for clearance, 2.5 mm for a tap drill. Here are the exact numbers and when to use each.
M3 clearance hole (screw passes through)
A clearance hole lets the M3 screw’s 3 mm shank slide straight through without binding. The standard sizes:
| Fit | Hole diameter | Use when |
|---|---|---|
| Close | 3.2 mm | Precise alignment, snug fit |
| Normal | 3.4 mm | Most general use |
| Loose | 3.6 mm | Easy assembly, some play |
When in doubt, 3.4 mm is the safe default. Need the same numbers for M4, M5, and up? The full table is in the metric clearance hole size chart, and the bolt-focused version is the bolt hole size chart.
M3 tapped hole (threading into the part)
To cut M3 threads directly into a part, you drill a smaller tap drill hole first, then run an M3 tap. For standard coarse M3 (0.5 mm pitch), the tap drill is 2.5 mm.
| Hole type | M3 diameter |
|---|---|
| Tap drill (coarse, 0.5 mm pitch) | 2.5 mm |
| Clearance (normal) | 3.4 mm |
Tapping works in metal. In plastic and 3D prints, cut threads strip easily — use a heat-set insert instead, which needs a straight hole sized to the insert. See heat-set inserts for 3D printing and how to add threads to a part.
M3 holes for 3D printing
Printed holes come out smaller than designed — the plastic squeezes inward and the first layer can sag. For a 3D-printed M3 clearance hole, start one size up (around 3.6–3.8 mm modeled) and test-fit; widen if the screw binds. The reasons and a general fit guide are in tolerances for 3D printed parts.
Designing the part that holds the hole? Mind the wall around it — see wall thickness for 3D printing.
Put an M3 hole in your part
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