51309-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 51309-SKF model number is decoded

The 51300 series order number 51309 is a SKF single-direction thrust ball bearing for a 45 mm seat, built to ISO 104, with a flat housing seating surface, 45×85×28 mm boundary dimensions. Three separable parts make the set: the tight-bore shaft washer that locates on the shaft, the loose-bore housing washer in its register, and the ball-cage assembly; load is purely axial and acts in one direction. reading 51xxx as a code: the 1 after 5 identifies one load direction and a flat seat, and the next digit ranks the section 1 (light) to 4 (heavy) before the two-digit bore code. bore code 09 decodes to 45 mm (code 09 × 5) under the same 00/01/02/03-exception, ×5 rule SKF uses across its coded bearing ranges. the suffix-free listing carries the catalogue default: a pressed (stamped sheet-steel) ball-cage assembly, light and quiet, used across the small and medium sizes. Envelope 45×85×28 mm (1.772×3.346×1.102 in), 20.0 mm radial section, C 76.1 kN, C0 153 kN, Pu 5.6 kN. reference speed 2,800 r/min (thermal) and limiting speed 4,000 r/min (mechanical), catalogue mass 660 g. Light-load floor: Pu = 5.6 kN is the equivalent-load threshold below which the SKF adjusted-life equation credits very long life for 51309; the number is 7 % of the 76.1 kN dynamic rating. Capacity density: 76.1 kN C from 0.660 kg of bearing steel gives about 115.3 kN per kilogram; static density is correspondingly 231.8 kN/kg at C0 153 kN. Section proportions: the 20.0 mm radial section compares with 45 mm of bore (section/bore ≈ 0.44) and the 28 mm height is 1.40× that section — the proportions that identify the 51300 envelope at a glance. Static-first selection data: 153 kN C0 spread across the 28 mm stack gives 5.5 kN of static rating per height millimetre, and the 660 g mass/C0 ratio is about 4 g per static kN — crane-hook and screw positions are normally sized on these two figures. Load balance: C0 153 kN against C 76.1 kN gives a 2.01 ratio — thrust ball bearings are chosen on static rating and F_a/C0 far more often than on L10 life, while Pu 5.6 kN enters the adjusted-life check. 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 45 mm size the pressed cage and separable washers make the bearing interchangeable across brands on the ISO 104 plan, but the SKF ratings 76.1/153 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

• 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 51309 against two-way load lifts the loose washer off its raceway.
• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 0.12; for 51309 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.
• The third digit grades the section: 511 light, then 512, 513 and 514 progressively taller and heavier at the same bore — select from 76.1/153 kN and the available 85 mm OD, never substitute a lighter series for a heavier one without rechecking C and C0.
• 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.
• Catalogue ratings are SKF PUB BU/P1 17000 figures for 51309 as the single flat pressed steel execution; other order numbers of the 51309 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.