51218-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 51218-SKF model number is decoded

51218 is SKF's 90 mm-bore single-direction thrust ball bearing in the 51200 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 90×135×35 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 18 encode the bore as 90 mm (code 18 × 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 90×135×35 mm (3.543×5.315×1.378 in), 22.5 mm radial section, C 112 kN, C0 290 kN, Pu 10.4 kN. reference speed 2,000 r/min (thermal) and limiting speed 2,800 r/min (mechanical), catalogue mass 1700 g. Sizing arithmetic on the 90 mm bore: 112 kN C over the 22.5 mm radial section gives 5.0 kN per section millimetre, and the 35 mm stack height is 1.56× that section — proportions typical of a 51200 thrust section. Envelope economics: the 35 mm axial height over a 22.5 mm radial section yields 3.2 kN of dynamic capacity per height millimetre, and the bearing weighs 1700 g for 112 kN C — about 15 g per rated kN. Pitch-diameter arithmetic: dm = (90+135)/2 = 112.5 mm; at the 2,800 r/min limiting speed that corresponds to roughly 315k mm·r/min, the figure used when comparing cage speed demand across the thrust-ball series. Mass and section check: 1700 g inside the 90×135×35 mm outline leaves a 22.5 mm radial section, and the 290 kN static rating is 2.59× the dynamic rating — plan static safety and minimum preload against those figures. Section proportions: the 22.5 mm radial section compares with 90 mm of bore (section/bore ≈ 0.25) and the 35 mm height is 1.56× that section — the proportions that identify the 51200 envelope at a glance. 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 35 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 112 kN C.

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 35 mm stack; thrust-ball bearings on horizontal shafts should have the shaft washer (the tight one) against the rotating element.
• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 90 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• 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 112 kN track before first rotation.
• 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 51218 as the single flat pressed steel execution; other order numbers of the 51218 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.