Metric Clearance Hole Size Chart
A clearance hole is a hole sized so a bolt passes straight through it without threading — the bolt is held by a nut or a tapped hole on the far side, not by the hole itself. Make it too tight and the bolt binds or won’t line up; too loose and the part slides around. This chart gives the close, normal, and loose clearance diameters for metric bolts M2 through M12, based on the standard ISO 273 fit classes.
Metric clearance hole chart (mm)
Pick a column by how precisely the parts must line up. Close for tight alignment, Normal for everyday assembly (use this if unsure), Loose when holes in two parts must still line up despite tolerance.
| Bolt | Close fit (mm) | Normal fit (mm) | Loose fit (mm) |
|---|---|---|---|
| M2 | 2.2 | 2.4 | 2.6 |
| M2.5 | 2.7 | 2.9 | 3.1 |
| M3 | 3.2 | 3.4 | 3.6 |
| M4 | 4.3 | 4.5 | 4.8 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7.0 |
| M8 | 8.4 | 9.0 | 10.0 |
| M10 | 10.5 | 11.0 | 12.0 |
| M12 | 13.0 | 13.5 | 14.5 |
These are the through-hole diameters for the bolt shaft. If you also need the bolt head to sit flush or recessed, that is a counterbore or countersink — see countersink vs counterbore for those diameters.
3D-printed holes need extra clearance
The chart above is for machined or drilled holes. A 3D printer almost always prints holes undersize — the inner walls bulge slightly inward and the first layer spreads. If you model an M3 normal-fit hole at 3.4 mm and print it, an M3 bolt often won’t pass.
Rule of thumb for FDM
Add 0.2–0.4 mm to the chart diameter for a printed clearance hole, or step up to the next size. For an M3 clearance hole on an FDM print, 3.6–3.8 mm usually drops a bolt straight through. Resin prints hold size better — add ~0.1 mm.
This is the same dimensional-accuracy issue covered in tolerances for 3D printed parts. If you need the bolt to thread into the part instead of passing through, that is a tap drill, not a clearance hole — see how to add threads to a part.
Clearance hole vs tapped hole
Every bolted joint has two holes. Know which one you are drawing:
Clearance hole (this chart)
The bolt passes through. Slightly larger than the bolt. Goes in the part that gets clamped down. Pairs with a nut or a tapped hole behind it.
Tapped / threaded hole
The bolt threads into it. Smaller than the bolt (the tap drill size) so threads can be cut. For an M3 that is a 2.5 mm hole, not 3.4 mm.
Mixing these up is the most common fastener mistake: a clearance-sized tapped hole has nothing to grip, and a tap-sized clearance hole won’t let the bolt through. For the bolt-head and nut side, the full reference is the bolt hole size chart for 3D printing.
How to pick a fit class
- Close fit — precision alignment, dowel-like location, single tight joint. Less forgiving of misalignment.
- Normal fit — the default for almost everything. Assembles easily, holds position. Use this when in doubt.
- Loose fit — when two separately-made parts must bolt together and their hole positions might not perfectly agree, or for thermal movement and field assembly.
Add clearance holes to your part
Tell PartWork.ai the bolt size and fit — “add four M4 clearance holes in a 60 mm square pattern” — and it places correctly-sized holes for you. Check the fit in the 3D viewer, then export STEP for a machine shop or STL/3MF for printing. See creating parts and exporting files.
Free to upload & view — sign up to download
Open the studio, describe your part and its bolt pattern, and export a file ready to make. More credits: 100 for $4.99 (~5¢ each).