51306-SKF bearing: complete specifications & equivalents

Specification table

Source: catalog reference (SKF PUB BU/P1 17000/1 EN (Oct 2018)) · extracted 2026-09-28

Parameters extracted from the official SKF Rolling Bearings catalogue (SKF PUB BU/P1 17000/1 EN (Oct 2018)); SKF® and SKF Explorer® are trademarks of AB SKF, used here for identification only — mpnbase is not an authorized SKF distributor. Boundary dimensions are ISO 15 interchangeable; current production values may differ, verify at skf.com.

Cross references & equivalents

Interchange levels: full standard interchange · partial verify parameters · verify manual confirmation required. Links resolve to the equivalent model's specification page where available.

How the 51306-SKF model number is decoded

51306 is SKF's 30 mm-bore single-direction thrust ball bearing in the 51300 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 30×60×21 mm. The separable set comprises a shaft washer (ground bore, tight fit on the shaft), a loose-bore housing washer and one ball-cage assembly, reacting axial force in one direction and carrying no radial load. in the 51xxx designation the first 1 marks a single-direction bearing with a flat housing seating surface; the third digit 1–4 grades the dimension series from the light 511 section through the heavy 514 section. the final two digits 06 encode the bore as 30 mm (code 06 × 5), the standard SKF bore-code rule shared with radial bearings. with no cage suffix this is the standard execution with a stamped sheet-steel ball-cage assembly (pressed cage) — the light, quiet and economical cage for small and medium thrust-ball sizes. Envelope 30×60×21 mm (1.181×2.362×0.827 in), 15.0 mm radial section, C 35.8 kN, C0 65.5 kN, Pu 2.4 kN. reference speed 3,800 r/min (thermal) and limiting speed 5,300 r/min (mechanical), catalogue mass 260 g. Bore-to-OD planning: OD 60 over bore 30 is a 2.00× step for this size, and the 21 mm height gives a bore/height ratio of 1.43; use these ratios when the housing recess around the 30 mm shaft is the first constraint. Envelope economics: the 21 mm axial height over a 15.0 mm radial section yields 1.7 kN of dynamic capacity per height millimetre, and the bearing weighs 260 g for 35.8 kN C — about 7 g per rated kN. Speed planning separates the two ceilings mechanically: the pressed cage and balls tolerate 5,300 r/min while thermal balance under catalogue load sets the 3,800 r/min reference; at dm ≈ 45.0 mm the corresponding dn is approximately 239k mm·r/min. Rating split for documentation: dynamic 35.8 kN (L10 life), static 65.5 kN (safety factor s0), fatigue limit 2.4 kN (adjusted life) — three different uses of three different numbers for 51306, none interchangeable with another. Section proportions: the 15.0 mm radial section compares with 30 mm of bore (section/bore ≈ 0.50) and the 21 mm height is 1.40× that section — the proportions that identify the 51300 envelope at a glance. Execution note for this order number: the flat housing seating surface must be machined square to the shaft axis and supported across the full washer face — unlike the sphered 53-series execution this pressed-cage 51-series bearing has no self-aligning capability at all, so seat squareness is checked at mounting, not compensated in service. On this 30 mm size the pressed cage and separable washers make the bearing interchangeable across brands on the ISO 104 plan, but the SKF ratings 35.8/65.5 kN are this catalogue's figures — confirm the replacement order's ratings rather than swapping on envelope alone.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• When the housing seat cannot be machined square to the 30 mm shaft, the sphered 53-series execution of this size with its U seat washer is the self-aligning counterpart of this flat 51300 bearing.
• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 30 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• On vertical shafts retain the loose housing washer positively with a cover or ring and verify the grease fill does not drain out of the 21 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• The three components are separable and interchangeable within the ISO 104 size, but keep this bearing's parts together in service and never combine washers from different manufacturers or a worn washer with a new ball set.
• Ordering discipline for 51306: the catalogue page quotes 51306 and its 35.8/65.5 kN ratings as one exact article; bare-number substitutions from another series or brand need a fresh dimension and rating check, not a like-for-like assumption.