Round Bore for the Race
Bearing Race Fit Parts

A bearing race fit part is any precision component that holds or interfaces with a bearing outer or inner race — including bearing housings, adapter rings, race carriers, and end caps. The bore tolerance of the housing (H7 for floating/sliding outer race, K6 or M6 for fixed outer race interference fit) directly determines the bearing preload, operating clearance, and whether the race can spin in service.

The fit depends on whether the outer race rotates relative to the load: Outer race stationary (most common): housing bore H7 — slight clearance to allow the outer race to shift thermally but prevent spinning; Outer race rotating (e.g., wheel hub bearings): housing bore K6 or M6 — slight interference to prevent race spinning under load. The specific tolerance depends on bearing size and radial load — always check the bearing manufacturer's fit recommendation.

Bearing housing bore roundness should be ≤ 50% of the bearing outer ring width tolerance as a rule of thumb — for most bearings, this means ≤ 0.005 mm roundness. Non-round housing bores cause the bearing outer race to distort into a non-circular shape, reducing internal clearance and changing ball contact angles, leading to premature fatigue. HXC achieves housing bore roundness ≤ 0.005 mm as standard.

Bearing housing bore surface finish: Ra 0.8 µm for standard interference fit (M6/K6) housings — this ensures consistent interference without local high spots that would create stress concentrations. Ra 1.6 µm is acceptable for clearance fit (H7) housings. For press-fitted sleeves or bearing rings that must be pulled out for maintenance: Ra 0.4 µm improves dimensional consistency of the pull-out force. HXC achieves all these finishes.

Prototype (1–5 pcs, turned + ground): 5–8 days. Small batch (10–50 pcs): 8–14 days. Production (100–1,000 pcs): 12–18 days. Stainless or titanium: add 2–4 days. Rush production available.

42CrMo4 (induction hardened) for industrial and automotive gearboxes. 20CrMnTi (carburized) for heavy industrial and wind. SUS303/316L stainless for food, pharma, marine. Al 6061/7075 hard-anodized for cobot and lightweight. GCr15/SUJ2 bearing steel for bearing-grade rings. Ti Grade 5 for aerospace.

Every batch ships with a Talyrond roundness trace + CMM dimensional report. Bore diameter is measured at three axial positions (front, mid, rear) and roundness is verified at each. Shoulder perpendicularity to bore is reported. For interference-fit (K6/M6) parts, the bore diameter histogram across the batch is included so the press-fit force is predictable.

Yes — bearing bore, retaining shoulder, oil-feed cross-holes, snap-ring grooves, seal lips, and external mounting features are all machined in the same setup, ensuring concentricity between bore and external features within 0.01 mm TIR.