51230-M 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 51230-M model number is decoded

Listed in SKF 17000 chapter 5, 51230 M is an ISO 104 single-direction thrust ball bearing, 150 mm bore and 215 mm OD on a flat housing seat, standing 50 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 30: bore 150 mm (code 30 × 5) for this single-direction size, via the standard exceptions 00/01/02/03 and ×5 above them. M-cage execution: brass machined from solid and ball-centred, giving heavier guidance than the standard pressed retainer at the top end of the thrust-ball range. Envelope 150×215×50 mm (5.906×8.465×1.969 in), 32.5 mm radial section, C 238 kN, C0 800 kN, Pu 22 kN. reference speed 1,300 r/min (thermal) and limiting speed 1,800 r/min (mechanical), catalogue mass 6100 g. Rating split for documentation: dynamic 238 kN (L10 life), static 800 kN (safety factor s0), fatigue limit 22 kN (adjusted life) — three different uses of three different numbers for 51230 M, none interchangeable with another. Washer-annulus check: the π/4·(D²−d²) contact annulus of 51230 M covers about 18,634 mm², distributing C0 800 kN over a mean track circle of π·dm ≈ 573 mm. Light-load floor: Pu = 22 kN is the equivalent-load threshold below which the SKF adjusted-life equation credits very long life for 51230 M; the number is 9 % of the 238 kN dynamic rating. Preload at the mechanical ceiling: repeating Fam ≈ A·(n·dm/1000)² with factor A 3.3 at the 1,800 r/min limiting speed raises the required axial preload to about 356.1 kN; the reference-speed value 185.7 kN is the thermal design point. Speed-ratio note for this exact unit: the reference speed is 1,300 r/min against a 1,800 r/min limiting speed, a reference-to-limit ratio of 0.72. Machined-cage order-number note: the M brass cage is a one-piece ball-centred window cage, chosen at the heavy end of the section for speed and shock duty; it is heavier and stiffer than the pressed-steel execution of the smaller sizes and tolerates interrupted lubrication far better, which is why the catalogue restricts the M suffix to the large bores. At 6100 g the machined brass cage represents a meaningful fraction of total mass; balancing checks on high-speed 150 mm vertical shafts should use the actual M-execution weight, not the lighter pressed-cage catalogue value.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• 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 50 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• 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 51230 against two-way load lifts the loose washer off its raceway.
• When the housing seat cannot be machined square to the 150 mm shaft, the sphered 53-series execution of this size with its U seat washer is the self-aligning counterpart of this flat 51200 bearing.
• 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 51230 M as the single flat brass execution; other order numbers of the 51230 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.