Bearing Fits

Sources: GOST 3325-85, Rolling bearings. Tolerance fields and technical requirements for the seats of shafts and housings. Fits: Appendix 5 Tables 1 and 3 (fits), Tables 8 and 9 (load type and regime), Table 3 (roughness), Table 4 (roundness and diameter variation), Tables 5 and 6 (shoulder runout). GOST 520-2011, Rolling bearings. General specifications: Tables 1–12 (bore and outside-diameter tolerances) and Tables 13–31 (tapered roller bearings). ISO 286 limits.

Method: what turns sets the load on each ring (Table 8): a ring that turns relative to the load has a circulating load and needs an interference fit; a ring the load stays on has a local load and can be a looser fit. The load and the bearing type pick the rows of Appendix 5 Tables 1 and 3. Each recommended field becomes limits (ISO 286), set against the bearing's mean bore or outside-diameter tolerance (GOST 520-2011, upper deviation 0): most interference = largest seat − smallest ring (shaft) or largest ring − smallest housing bore; least = the other two limits; a negative value is clearance. The fits are shown loosest to tightest by the middle of that range. The closer-seat note names the same field one grade finer only where the same row prints it for class 5 and 4 bearings. Roundness, diameter variation and shoulder runout are read from Tables 4–6 by bearing class and diameter band; on the inch setting they and the roughness show in µin (1 µm = 39.37 µin) with the standard's µm beside them. Table 6 prints 30 µm for class 4 over 315 to 400 mm; the page uses 18 µm, the column's ISO grade (IT4), and says so.