51308-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 51308-SKF model number is decoded

51308 is SKF's 40 mm-bore single-direction thrust ball bearing in the 51300 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 40×78×26 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 08 encode the bore as 40 mm (code 08 × 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 40×78×26 mm (1.575×3.071×1.024 in), 19.0 mm radial section, C 61.8 kN, C0 122 kN, Pu 4.5 kN. reference speed 3,000 r/min (thermal) and limiting speed 4,300 r/min (mechanical), catalogue mass 530 g. Mass and section check: 530 g inside the 40×78×26 mm outline leaves a 19.0 mm radial section, and the 122 kN static rating is 1.97× the dynamic rating — plan static safety and minimum preload against those figures. Envelope economics: the 26 mm axial height over a 19.0 mm radial section yields 2.4 kN of dynamic capacity per height millimetre, and the bearing weighs 530 g for 61.8 kN C — about 9 g per rated kN. Minimum-load arithmetic: with dm ≈ 59.0 mm and factor A 0.077, Fam ≈ A·(n·dm/1000)² at the 3,000 r/min reference speed is about 2.4 kN for 51308; below that preload the balls skid and smear the tracks. Imperial cross-check for procurement drawings: 1.575 in bore, 3.071 in OD, 1.024 in height, and the 530 g catalogue mass converts to 0.530 kg (18.7 oz). Rating split for documentation: dynamic 61.8 kN (L10 life), static 122 kN (safety factor s0), fatigue limit 4.5 kN (adjusted life) — three different uses of three different numbers for 51308, none interchangeable with another. 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. Inspection after removal of a 26 mm-high stack means checking both washer faces: the loose housing washer often shows the first false-brinell marks under machine vibration even though the tight shaft washer carries the rotating load of 61.8 kN C.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 40 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• The 51308 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 40 mm shaft has to be carried by a radial bearing mounted alongside it.
• 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.
• When the housing seat cannot be machined square to the 40 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.
• The 61.8/122 kN figures belong to 51308 specifically (the single flat pressed steel execution of 51308); suffixed, sphered and counterpart-series order numbers are separate articles, so write the complete designation on the order and the maintenance record.