51220-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 51220-SKF model number is decoded

Listed in SKF 17000 chapter 5, 51220 is an ISO 104 single-direction thrust ball bearing, 100 mm bore and 150 mm OD on a flat housing seat, standing 38 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 20: bore 100 mm (code 20 × 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 100×150×38 mm (3.937×5.906×1.496 in), 25.0 mm radial section, C 119 kN, C0 325 kN, Pu 10.8 kN. reference speed 1,800 r/min (thermal) and limiting speed 2,400 r/min (mechanical), catalogue mass 2200 g. Bore-to-OD planning: OD 150 over bore 100 is a 1.50× step for this size, and the 38 mm height gives a bore/height ratio of 2.63; use these ratios when the housing recess around the 100 mm shaft is the first constraint. Sizing arithmetic on the 100 mm bore: 119 kN C over the 25.0 mm radial section gives 4.8 kN per section millimetre, and the 38 mm stack height is 1.52× that section — proportions typical of a 51200 thrust section. Load balance: C0 325 kN against C 119 kN gives a 2.73 ratio — thrust ball bearings are chosen on static rating and F_a/C0 far more often than on L10 life, while Pu 10.8 kN enters the adjusted-life check. Stack/annulus proportions: the 38 mm axial stack over the 9,817 mm² washer annulus gives 3.87 mm of height per annular square millimetre ×10⁻³, and at 2200 g the bearing holds about 147.7 kN of C0 per kilogram. Mass and section check: 2200 g inside the 100×150×38 mm outline leaves a 25.0 mm radial section, and the 325 kN static rating is 2.73× the dynamic rating — plan static safety and minimum preload against those figures. 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 38 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 119 kN C.

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 51220 against two-way load lifts the loose washer off its raceway.
• When the housing seat cannot be machined square to the 100 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.
• 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 38 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 100 mm shaft, while the housing washer bore is larger and runs loose; swapping them locks the ball set and burns the tracks.
• Catalogue ratings are SKF PUB BU/P1 17000 figures for 51220 as the single flat pressed steel execution; other order numbers of the 51220 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.