51120-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 51120-SKF model number is decoded

51120 is SKF's 100 mm-bore single-direction thrust ball bearing in the 51100 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 100×135×25 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 20 encode the bore as 100 mm (code 20 × 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 100×135×25 mm (3.937×5.315×0.984 in), 17.5 mm radial section, C 80.6 kN, C0 265 kN, Pu 9.15 kN. reference speed 2,400 r/min (thermal) and limiting speed 3,200 r/min (mechanical), catalogue mass 970 g. Preload at the mechanical ceiling: repeating Fam ≈ A·(n·dm/1000)² with factor A 0.44 at the 3,200 r/min limiting speed raises the required axial preload to about 62.2 kN; the reference-speed value 35.0 kN is the thermal design point. Bore-to-OD planning: OD 135 over bore 100 is a 1.35× step for this size, and the 25 mm height gives a bore/height ratio of 4.00; use these ratios when the housing recess around the 100 mm shaft is the first constraint. Rating split for documentation: dynamic 80.6 kN (L10 life), static 265 kN (safety factor s0), fatigue limit 9.15 kN (adjusted life) — three different uses of three different numbers for 51120, none interchangeable with another. Capacity density: 80.6 kN C from 0.970 kg of bearing steel gives about 83.1 kN per kilogram; static density is correspondingly 273.2 kN/kg at C0 265 kN. Track-circle loading: per millimetre of mean track circumference the 80.6 kN dynamic rating corresponds to roughly 0.22 kN/mm of π·dm track, a useful comparison against the other dimension series of the 100 mm bore. 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 25 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 80.6 kN C.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• The 51120 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 100 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 51120 against two-way load lifts the loose washer off its raceway.
• 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.
• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 0.44; for 51120 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.
• Catalogue ratings are SKF PUB BU/P1 17000 figures for 51120 as the single flat pressed steel execution; other order numbers of the 51120 size are different products and may carry different ratings or seating geometry — always quote the full designation when purchasing.