FitCheck

Find the right hole size for the machine making the part.

Every machine cuts a bit differently

The standard clearance charts are fine as a baseline, but it's frustrating when you design around those baselines and still have to reprint a part a few times to get the hole right, re-mill it because a bolt won't pass through, or bore a bearing seat twice because the first one wouldn't hold. FitCheck fixes that by taking your actual machine's accuracy into account.

Calibrate each machine, save it, and every number the app gives you comes out already corrected for that machine. The correction is per-dimension, not one global offset: round holes and hex pockets print with different errors, and big bores run differently than small holes, so a single slicer-wide hole compensation can't get every fit rig

What you get

60 metric and imperial thread sizes, 9 common bearings (the 608/623/625/695 family, their flanged versions, and a spherical pivot bearing), and the matching hex nuts - all on your phone. Type in what you're fitting - M3, M5-0.8, #8-32, 1/4-20, or 608 for a bearing - pick what you're using, and you get:

Additive · FDM

  • Clearance hole - close, normal, or free fit

  • Thread into plastic - the self-tap pilot hole for screwing straight into plastic

  • Heat-set insert pocket - diameter plus short, standard, and long depths

  • Hex nut pocket - a captive pocket for the matching nut, in snug, normal, and loose grades (metric M1.6–M6)

  • Printed bearing pocket - offsets a printer can actually hold, not machinist micron grades

  • Robust pocket - nut and bearing pockets with crush ribs that grip without calibration, for models that print on machines you haven't measured

  • Head recess - a recess the screw head actually clears

  • A cross-section diagram - the bolt in the hole, the insert in its pocket, the bearing in its seat

Subtractive · CNC

  • Clearance hole - close, normal, or free fit, with the drill size

  • Tap drill - the hole to model before you cut threads

  • Counterbore - the head sits flush and clears

  • Machined bearing seat - press, slip, and loose housing fits

  • A cross-section diagram for clarity

And there's more to come - I've got a long list of features I want to add.

Calibrate in the app

Print the free calibration model for your machine (FDM and CNC models are available), measure a few holes with calipers, and enter the averages - FitCheck works out how far off your machine runs and corrects the holes and pockets it shows you from there. Printers can go finer with two optional measurements: a large bore so big holes get their own correction, and hex pockets so flat walls get theirs. The calibration guide walks through every step.

Run more than one machine? Save them all and switch the active one right from the lookup screen - the corrected numbers follow the machine you pick. And when a printer's calibration gets old, the app tells you it's due for a redo.

Calibration is free to try: add a machine, enter your measurement, and the clearance and pocket diameters shift immediately. Saving a machine so it persists between sessions is FitCheck Pro; with no machine active, you always get the standard numbers.

Inch ↔ mm conversions

The other thing I was always looking up. The Fractions tab converts between inches and mm both ways and has a 64ths ruler, so a caliper or ruler reading gets you a usable number faster.

Offline and private

  • Works fully offline - the whole catalog is loaded on your device.

  • No account, no ads, no tracking - nothing leaves your device unless you turn on optional, anonymous calibration sharing (off by default).

  • The numbers come from published standards - ISO 273 and ASME B18.2.8 for clearance holes, ISO 4762/ASME B18.3 for screw heads, DIN 934 for hex nuts, and the ISO 286 fits for bearing seats. Heat-set insert pockets have no standard, so those follow the published insert design guidelines instead. Other pocket clearances are our own engineering call, the app labels those a recommendation.

Pricing

Looking up every size in the catalog is free, including trying calibration on any machine. FitCheck Pro saves your calibrated machines, so their offsets are applied automatically each time you open the app - a one-time purchase, no subscription.

Double-check!

This is a reference app, and fasteners hold things together - double-check anything important against the standard and a test part.

Have more questions? See the FitCheck support and FAQ page

Other resources

FitCheck is a product of Baked Bean LLC (d/b/a BakedBean3D), Illinois, USA.