Bolt Hole Size Chart for 3D Printing
Pick the wrong hole size and your bolt either will not fit or strips out the plastic. Here is a plain chart for M3, M4, and M5 — the three most common sizes in 3D printed projects — plus when to tap the hole, use a nut, or grab a heat-set insert.
Clearance vs. tapped holes
There are two kinds of bolt hole, and getting them mixed up is the usual mistake:
Clearance hole
The bolt passes straight through with room to spare. The bolt head and a nut (or a threaded part underneath) do the clamping.
Tapped / threaded hole
The bolt cuts or follows threads in the part itself. Workable in plastic for light loads, but a heat-set insert is far stronger.
The chart
Sizes below already include a little extra for FDM shrinkage (see 3D print tolerances). Start here and adjust to your printer.
| Bolt | Clearance hole (Ø) | Self-tap hole (Ø) | Heat-set insert (Ø) |
|---|---|---|---|
| M3 | 3.4 mm | 2.5 mm | 4.0–4.2 mm |
| M4 | 4.5 mm | 3.3 mm | 5.6 mm |
| M5 | 5.5 mm | 4.2 mm | 6.4 mm |
For most projects, use clearance holes + nuts
A clearance hole with a captured hex nut is stronger and more reusable than threading into raw plastic. Heat-set inserts are best when you will unscrew the bolt many times.
Add the holes in seconds
With PartWork.ai you do not look any of this up at modeling time — describe the bolt and let the part update. Select a face and say:
Add four 3.4 mm clearance holes for M3 bolts, one in each corner, 5 mm from the edgesWant a counterbore so the bolt head sits flush? Ask for it: "counterbore the holes for M3 socket-head caps." See Creating Parts for prompt tips and Exporting when the part is ready.
Design a part with the right holes
Start with 2 free AI generations — no card required
Describe the part and the bolts it needs to take, get editable 3D geometry, export an STL. Open the studio. Need more after your free generations? 100 credits for $4.99 (about 5¢ each).