A fit where the shaft diameter exceeds the hole diameter, requiring force or temperature differential for assembly and creating a permanent friction bond.
Interference = shaft_min − hole_max > 0. Assembly stress is generated by elastic deformation. ISO codes: H7/p6 (light press), H7/s6 (heavy press). The interference determines the joint holding force via friction. Polymer parts have lower elastic modulus than metal, so interference values must be recalculated.
Used to permanently lock bushings, bearing races, and inserts. For FDM, heat-set brass inserts use thermal interference: the hot insert displaces melted plastic, which solidifies around knurls. Cold press-fit in FDM works best on short engagement lengths (≤2× diameter).
Over-interference in FDM splits the printed part along layer lines. Always prototype the interference fit before production. Creep at elevated temperature reduces clamp force over time: do not rely on polymer press-fits under sustained heat.
Related terms: Clearance Fit, Press Fit, Tolerance
| Field | engineering |
|---|---|
| Also called | press fit, force fit, shrink fit |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert