51209-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 51209-SKF model number is decoded

51209 is SKF's 45 mm-bore single-direction thrust ball bearing in the 51200 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 45×73×20 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 09 encode the bore as 45 mm (code 09 × 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 45×73×20 mm (1.772×2.874×0.787 in), 14.0 mm radial section, C 39 kN, C0 86.5 kN, Pu 3.2 kN. reference speed 3,600 r/min (thermal) and limiting speed 5,000 r/min (mechanical), catalogue mass 300 g. Load balance: C0 86.5 kN against C 39 kN gives a 2.22 ratio — thrust ball bearings are chosen on static rating and F_a/C0 far more often than on L10 life, while Pu 3.2 kN enters the adjusted-life check. Static-first selection data: 86.5 kN C0 spread across the 20 mm stack gives 4.3 kN of static rating per height millimetre, and the 300 g mass/C0 ratio is about 3 g per static kN — crane-hook and screw positions are normally sized on these two figures. Speed band width for this size is 1,400 r/min between reference and limiting (1.39× ratio); lubrication, preload and heat removal decide where inside that band 51209 can actually run. Sizing arithmetic on the 45 mm bore: 39 kN C over the 14.0 mm radial section gives 2.8 kN per section millimetre, and the 20 mm stack height is 1.43× that section — proportions typical of a 51200 thrust section. Track-circle loading: per millimetre of mean track circumference the 39 kN dynamic rating corresponds to roughly 0.21 kN/mm of π·dm track, a useful comparison against the other dimension series of the 45 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 20 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 39 kN C.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• When the housing seat cannot be machined square to the 45 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.
• Identify the washers before fitting: the shaft washer has the ground, smaller bore and takes an interference fit on the 45 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 0.038; for 51209 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.
• Ordering discipline for 51209: the catalogue page quotes 51209 and its 39/86.5 kN ratings as one exact article; bare-number substitutions from another series or brand need a fresh dimension and rating check, not a like-for-like assumption.