Screw hole calculator (ISO 273)
What hole diameter does an M4 screw need in a 3D-printed part? The standard sizes per ISO 273, plus a print allowance for the typical FDM hole shrinkage.
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Close, medium or large — which fit?
ISO 273 defines three series: close for precise, low-clearance connections, medium as the standard choice for most applications, large when more tolerance is needed or multiple parts have to align. For M4, that's 4.3 / 4.5 / 4.8 mm, for example — the difference is small, but noticeable on a tightly fitted screw.
Why an extra print allowance is needed
FDM holes often come out slightly smaller than in the model due to the printer's manufacturing tolerance. The allowance here is added to the total diameter — not per side — so a 0.2 mm allowance directly and visibly increases the hole diameter.
Countersink and socket head not yet included
For countersunk or socket-head-screw clearances, we currently lack verified standard values for the head dimensions. Rather than show unverified numbers, we'll add this once that data is verified.