51208-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 51208-SKF model number is decoded

51208 is SKF's 40 mm-bore single-direction thrust ball bearing in the 51200 series to the ISO 104 dimension plan, with a flat housing seating surface, measuring 40×68×19 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 08 encode the bore as 40 mm (code 08 × 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 40×68×19 mm (1.575×2.677×0.748 in), 14.0 mm radial section, C 44.2 kN, C0 96.5 kN, Pu 3.6 kN. reference speed 3,800 r/min (thermal) and limiting speed 5,300 r/min (mechanical), catalogue mass 280 g. Speed-ratio note for this exact unit: the reference speed is 3,800 r/min against a 5,300 r/min limiting speed, a reference-to-limit ratio of 0.72. Stack/annulus proportions: the 19 mm axial stack over the 2,375 mm² washer annulus gives 8.00 mm of height per annular square millimetre ×10⁻³, and at 280 g the bearing holds about 344.6 kN of C0 per kilogram. Light-load floor: Pu = 3.6 kN is the equivalent-load threshold below which the SKF adjusted-life equation credits very long life for 51208; the number is 8 % of the 44.2 kN dynamic rating. Capacity density: 44.2 kN C from 0.280 kg of bearing steel gives about 157.9 kN per kilogram; static density is correspondingly 344.6 kN/kg at C0 96.5 kN. Track-circle loading: per millimetre of mean track circumference the 44.2 kN dynamic rating corresponds to roughly 0.26 kN/mm of π·dm track, a useful comparison against the other dimension series of the 40 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 19 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 44.2 kN C.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 0.058; for 51208 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.
• 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 51208 against two-way load lifts the loose washer off its raceway.
• 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.
• The 51208 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 40 mm shaft has to be carried by a radial bearing mounted alongside it.
• Ordering discipline for 51208: the catalogue page quotes 51208 and its 44.2/96.5 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.