What fit class should I choose for a bearing?

For standard ball bearings pressed into a 3D printed housing, use FN1 (light press fit). The slight interference ensures the bearing stays in place. For bearings that need to be removable, use LT2 (tight transition).

How do clearance fits differ from press fits?

Clearance fits (RC classes) have a positive gap — the printed hole is larger than the printed shaft, so the parts slide or rotate freely (this tool targets roughly 0.15mm for a close fit up to 0.45mm for an easy fit). Press fits (FN classes) are interference fits: the printed shaft is LARGER than the printed hole (a negative gap, around -0.1 to -0.2mm here), so they must be forced together and hold by friction.

Why add printer tolerance compensation?

FDM holes print 0.1-0.3mm undersize and shafts print oversize because the nozzle path adds material on the inside of holes and the outside of pegs. To hit the intended fit, this tool enlarges the modelled hole and shrinks the modelled shaft by your calibration tolerance. Because the same amount is added to the hole and removed from the shaft, it cancels out of the realised gap — the target fit is unchanged, only the dimensions you actually model change. Set the tolerance from a printed test coupon for your machine and filament.

Do transition fits work well in 3D printing?

Yes, transition fits are actually ideal for many 3D printed assemblies. They allow hand-assembly but hold position well. The slight material flexibility of most 3D print materials helps create a forgiving but secure fit.

Fit Calculator

Fit Calculator — Press, Transition & Clearance Fits

Determine press-fit, transition-fit and clearance-fit dimensions for printed parts.

Nominal Diameter

The shared target diameter of the shaft and hole

Printer Tolerance

Per-machine calibration offset (FDM holes print undersize, shafts oversize). Typical 0.05–0.2mm; measure a test coupon.

Fit ClassRC = sliding/running clearance, LT = hand-assembled transition, FN = pressed-together interference

How We Calculate This

Fit Class Formulas

Hole diameter to model = Nominal + (Target gap / 2) + Printer tolerance
Shaft diameter to model = Nominal − (Target gap / 2) − Printer tolerance
Realised fit (printed) = Target gap (positive = clearance, negative = interference)

Each fit class carries a target diametral gap — the difference between the printed hole and printed shaft. The tool splits that gap symmetrically about the nominal diameter, then applies your printer-calibration tolerance to enlarge the modelled hole and shrink the modelled shaft (FDM holes print undersize, shafts print oversize). Because that compensation is equal and opposite, it cancels out of the realised fit, leaving exactly the target gap.

RC classes give clearance fits (positive gap, ~0.15–0.45mm) so parts slide or rotate freely. LT classes give transition fits (line-to-line, ~0 to +0.05mm) for hand-assembled, position-holding joints. FN classes give interference/press fits (negative gap, −0.1 to −0.2mm) where the shaft is larger than the hole and parts must be pressed together.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Always verify settings with test prints before committing to final prints.

Fit Calculator — Press, Transition & Clearance Fits

How We Calculate This

Fit Class Formulas

Frequently Asked Questions

Related Calculators

Scale Calculator

Tolerance Calculator

Shrinkage Calculator

Clearance Calculator

Wall Gap Calculator