51248-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 51248-M model number is decoded

Listed in SKF 17000 chapter 5, 51248 M is an ISO 104 single-direction thrust ball bearing, 240 mm bore and 340 mm OD on a flat housing seat, standing 78 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 48: bore 240 mm (code 48 × 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 240×340×78 mm (9.449×13.386×3.071 in), 50.0 mm radial section, C 449 kN, C0 1960 kN, Pu 42.5 kN. reference speed 800 r/min (thermal) and limiting speed 1,100 r/min (mechanical), catalogue mass 23000 g. Stack/annulus proportions: the 78 mm axial stack over the 45,553 mm² washer annulus gives 1.71 mm of height per annular square millimetre ×10⁻³, and at 23000 g the bearing holds about 85.2 kN of C0 per kilogram. Imperial cross-check for procurement drawings: 9.449 in bore, 13.386 in OD, 3.071 in height, and the 23000 g catalogue mass converts to 23.000 kg (811.3 oz). Preload at the mechanical ceiling: repeating Fam ≈ A·(n·dm/1000)² with factor A 21 at the 1,100 r/min limiting speed raises the required axial preload to about 2137.0 kN; the reference-speed value 1130.3 kN is the thermal design point. Speed band width for this size is 300 r/min between reference and limiting (1.38× ratio); lubrication, preload and heat removal decide where inside that band 51248 M can actually run. Envelope economics: the 78 mm axial height over a 50.0 mm radial section yields 5.8 kN of dynamic capacity per height millimetre, and the bearing weighs 23000 g for 449 kN C — about 51 g per rated kN. 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. The M cage of 51248 M adds a small amount of mass and cage strength without changing the 240×340×78 mm ISO 104 envelope, so the pressed-cage execution drops into the same recess but should not be assumed equal under the 1,100 r/min ceiling.

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 78 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• Heat the shaft washer to at most 120 °C for mounting, or press it via a sleeve on its ground bore — force applied through the housing washer or the ball set brinells the 449 kN track before first rotation.
• The 51248 M is a pure axial bearing: it must never be subjected to radial load — any radial force on the 240 mm shaft has to be carried by a radial bearing mounted alongside it.
• 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 51248 against two-way load lifts the loose washer off its raceway.
• Catalogue ratings are SKF PUB BU/P1 17000 figures for 51248 M as the single flat brass execution; other order numbers of the 51248 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.