FitCheck: Hole Sizes & Fits

"What size hole do I need for this screw?" That's the question FitCheck helps answer. Enter a screw or bolt — M5-0.8, #8-32, 1/4-20 — and it gives you the hole size to model, whether you're drilling, tapping, or screwing into plastic. For makers, hobbyists, and anyone who designs and builds with screws and hardware in mind: • Clearance holes and tap-drill sizes for every screw and bolt in the catalog (ISO 273 / ASME B18.2.8) • 3D-printing hole sizes that account for printer tolerances • Heat-set insert holes, with pocket depths matched to your insert length • An inch-to-mm converter and fraction ruler for quickly getting value from caliper or tape-measure readings • A cross-section diagram showing how the screw will interact with the hole or insert The part a standard conversion chart can't do: account for your machine's unique tolerances. Calibrate a machine once with FitCheck's calibration model, and every hole size comes out corrected for that machine — less re-printing or re-milling parts to get it right. It works completely offline. No accounts, no ads, and no tracking — all reference data lives on your device. FitCheck Pro is a one-time purchase, no subscription: it unlocks saving each machine's unique offset so it's applied automatically to every size you look up. This app is a reference only — always check against your own test parts before you cut.