51204-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 51204-SKF model number is decoded

The 51200 series order number 51204 is a SKF single-direction thrust ball bearing for a 20 mm seat, built to ISO 104, with a flat housing seating surface, 20×40×14 mm boundary dimensions. Three separable parts make the set: the tight-bore shaft washer that locates on the shaft, the loose-bore housing washer in its register, and the ball-cage assembly; load is purely axial and acts in one direction. reading 51xxx as a code: the 1 after 5 identifies one load direction and a flat seat, and the next digit ranks the section 1 (light) to 4 (heavy) before the two-digit bore code. bore code 04 decodes to 20 mm (code 04 × 5) under the same 00/01/02/03-exception, ×5 rule SKF uses across its coded bearing ranges. the suffix-free listing carries the catalogue default: a pressed (stamped sheet-steel) ball-cage assembly, light and quiet, used across the small and medium sizes. Envelope 20×40×14 mm (0.787×1.575×0.551 in), 10.0 mm radial section, C 21.2 kN, C0 37.5 kN, Pu 1.4 kN. reference speed 6,000 r/min (thermal) and limiting speed 8,000 r/min (mechanical), catalogue mass 83 g. Mass and section check: 83 g inside the 20×40×14 mm outline leaves a 10.0 mm radial section, and the 37.5 kN static rating is 1.77× the dynamic rating — plan static safety and minimum preload against those figures. Speed band width for this size is 2,000 r/min between reference and limiting (1.33× ratio); lubrication, preload and heat removal decide where inside that band 51204 can actually run. At the printed limiting speed of 8,000 r/min the mean pitch diameter dm ≈ 30.0 mm implies a dn value around 240k mm·r/min; the 6,000 r/min reference speed is the thermal-planning value under catalogue load. Stack/annulus proportions: the 14 mm axial stack over the 942 mm² washer annulus gives 14.86 mm of height per annular square millimetre ×10⁻³, and at 83 g the bearing holds about 451.8 kN of C0 per kilogram. Speed planning separates the two ceilings mechanically: the pressed cage and balls tolerate 8,000 r/min while thermal balance under catalogue load sets the 6,000 r/min reference; at dm ≈ 30.0 mm the corresponding dn is approximately 240k mm·r/min. 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. On this 20 mm size the pressed cage and separable washers make the bearing interchangeable across brands on the ISO 104 plan, but the SKF ratings 21.2/37.5 kN are this catalogue's figures — confirm the replacement order's ratings rather than swapping on envelope alone.

Typical equipment & failure modes

Selection pitfalls — read before you substitute

• When the housing seat cannot be machined square to the 20 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.
• Keep the applied thrust above Fam ≈ A·(n·dm/1000)² with the printed factor A 0.0085; for 51204 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.
• The third digit grades the section: 511 light, then 512, 513 and 514 progressively taller and heavier at the same bore — select from 21.2/37.5 kN and the available 40 mm OD, never substitute a lighter series for a heavier one without rechecking C and C0.
• The 51204 is a pure axial bearing: it must never be subjected to radial load — any radial force on the 20 mm shaft has to be carried by a radial bearing mounted alongside it.
• Ordering discipline for 51204: the catalogue page quotes 51204 and its 21.2/37.5 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.