51305-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 51305-SKF model number is decoded

Listed in SKF 17000 chapter 5, 51305 is an ISO 104 single-direction thrust ball bearing, 25 mm bore and 52 mm OD on a flat housing seat, standing 18 mm high before installation. The bearing is delivered as separate, interchangeable parts: a ground-bore shaft washer, a loose-bore housing washer and the ball-cage assembly between them, designed for one axial load direction only. 51xxx breaks down as 5 for thrust ball, 1 for one load direction on a flat seat, a section digit 1–4 light-to-heavy, then the two-digit bore code. reading the ending 05: bore 25 mm (code 05 × 5) for this single-direction size, via the standard exceptions 00/01/02/03 and ×5 above them. no cage suffix means the standard stamped steel retainer — a pressed sheet-metal ball-cage assembly that covers the bulk of the thrust-ball assortment. Envelope 25×52×18 mm (0.984×2.047×0.709 in), 13.5 mm radial section, C 34.5 kN, C0 60 kN, Pu 2.24 kN. reference speed 4,500 r/min (thermal) and limiting speed 6,300 r/min (mechanical), catalogue mass 170 g. Bore-to-OD planning: OD 52 over bore 25 is a 2.08× step for this size, and the 18 mm height gives a bore/height ratio of 1.39; use these ratios when the housing recess around the 25 mm shaft is the first constraint. Light-load floor: Pu = 2.24 kN is the equivalent-load threshold below which the SKF adjusted-life equation credits very long life for 51305; the number is 6 % of the 34.5 kN dynamic rating. Mass and section check: 170 g inside the 25×52×18 mm outline leaves a 13.5 mm radial section, and the 60 kN static rating is 1.74× the dynamic rating — plan static safety and minimum preload against those figures. Speed band width for this size is 1,800 r/min between reference and limiting (1.40× ratio); lubrication, preload and heat removal decide where inside that band 51305 can actually run. Minimum-load arithmetic: with dm ≈ 38.5 mm and factor A 0.018, Fam ≈ A·(n·dm/1000)² at the 4,500 r/min reference speed is about 540 N for 51305; below that preload the balls skid and smear the tracks. 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 18 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 34.5 kN C.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• The third digit grades the section: 511 light, then 512, 513 and 514 progressively taller and heavier at the same bore — select from 34.5/60 kN and the available 52 mm OD, never substitute a lighter series for a heavier one without rechecking C and C0.
• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 0.018; for 51305 a spring preload or the rotor weight is part of the selection at light load and high speed, because unloaded balls skid rather than roll.
• A 51-series bearing reacts thrust in one direction only — reversing positions need a mirrored single-direction pair or a 52-series double-direction unit; fitting a single 51305 against two-way load lifts the loose washer off its raceway.
• 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 18 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• Ordering discipline for 51305: the catalogue page quotes 51305 and its 34.5/60 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.