A fit where the shaft is always smaller than the hole, guaranteeing a positive gap for free assembly or motion.
Clearance = hole_min − shaft_max > 0. ISO system uses letter codes: H7/f6 (running), H7/g6 (sliding). Minimum clearance guarantees assembly; maximum clearance determines play. For FDM parts, add 0.2–0.4 mm extra clearance per side due to dimensional error and surface roughness.
Bearing housings, rotating pins, and drawer slides use clearance fits. In 3D printing, print-in-place hinges need 0.3–0.5 mm clearance per side. Test with a calibration print before committing final geometry.
Thermal expansion of polymers can reduce clearance at elevated temperatures. PLA softens at ~60°C; ABS at ~95°C. Size clearances for the worst-case operating temperature, not just room temperature.
Related terms: Interference Fit, Tolerance, Assembly Clearance, Press Fit
| Field | engineering |
|---|---|
| Also called | running fit, sliding fit |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert