FitCheck: Hole Sizes & Fits

"What size hole do I need?" That's the question FitCheck answers for screws, bearings, and hex nuts. Enter a size, like M5-0.8, #8-32, 1/4-20, or 608 bearing, and you get the hole or pocket to model: drilled, tapped, bored for a bearing, or printed.

In the app:
• Clearance holes and tap-drill sizes for every screw and bolt in the catalog
• Counterbore and head-recess sizes for socket and button head screws (button heads M3–M16 and #2–5/8)
• Bearing pockets: press, slip, and loose fits for machined and 3D printed seats
• Hex-nut pockets in three clearances (snug/normal/loose)
• Robust pockets: crush-rib pockets that grip without calibration - tested on every catalog bearing (Ø10–22 mm) and five nut sizes (M2.5–M6)
• 3D-printed screw holes in three grades (close/normal/free)
• Heat-set insert holes with pocket depths matched to your insert length
• An inch-to-mm converter and fraction ruler for caliper readings
• Cross-section diagrams that show the fit or what to model
• Star your go-to sizes - favorites and your recent lookups live on the home screen

The part a chart can't do: adjust to your machine. Calibrate each printer or mill in the app and the clearance and pocket sizes come out corrected for that machine's measured error.

Round holes and hex pockets don't miss by the same amount, so FitCheck has you measure them separately, and each one gets corrected on its own axis. Big bores are different again: measure the large bore on the calibration part too, and each diameter corrects at its own size. Less re-printing and re-milling to get a fit right.

It works offline by default. No accounts, no ads, and nothing leaves your device unless you turn on optional, anonymous calibration sharing.

Machine calibration is free to try. FitCheck Pro - a one-time purchase, no subscription - keeps your calibrated machines saved, so every lookup comes out corrected without redoing setup.

This app is a reference only - always check against your own test parts before you cut.