51204 Bearing — Cross-Reference & Equivalents
The 51204 is a thrust ball bearing with ISO 104 boundary dimensions 20×40×14 mm. The table below lists how 8 major brands designate it, with catalog links and interchange notes.
Replacing a 51204? The cross-reference table below gives the equivalent part number for every major brand — but read the interchange rules first: an identical size is not always a safe swap.
Specifications
| Bore (d) | 20 mm |
|---|---|
| Outer Diameter (D) | 40 mm |
| Height (H) | 14 mm |
| Type | Thrust Ball Bearing |
| Standard | ISO 104 |
Cross-Reference by Brand
| Brand | Part No. | Boundary dims | Catalog |
|---|---|---|---|
| SKF | 51204 | match | SKF catalog ↗ |
| NSK | 51204 | match | NSK catalog ↗ |
| FAG | 51204 | match | FAG catalog ↗ |
| NTN | 51204 | match | NTN catalog ↗ |
| KOYO | 51204 | match | KOYO catalog ↗ |
| NACHI | 51204 | match | NACHI catalog ↗ |
| Timken | 51204 | match | Timken catalog ↗ |
| INA | 51204 | match | INA catalog ↗ |
Interchange notes
All brands build this designation to the same ISO 104 boundary dimensions (d, D, H), so the mounting envelope is interchangeable. But a thrust ball bearing is an AXIAL bearing and matching dimensions is far from enough: (1) It carries pure axial (thrust) load in ONE direction only and supports NO radial load — despite matching bore/OD it is functionally unrelated to a same-size radial ball bearing and must never replace one. (2) It is three separate parts — a shaft washer (tight on the shaft), a housing washer (loose in the housing) and the ball-and-cage set; installing the washers reversed fails fast. (3) Single-direction (51xxx) and double-direction (52xxx, with a centre washer) differ in stack height and are not interchangeable. (4) A minimum axial preload is required — at low load and high speed the balls skid and fail early. (5) Aligning-seat (spherical-seat) variants are not dimensionally equal to flat-seat types; match clearance, precision class and cage. Load ratings (dynamic Cr, static C0r) are intentionally NOT listed here: they vary by brand and internal design and are a safety-critical selection parameter — read them directly from the manufacturer catalog linked in the table above.
Where to buy a 51204
Compare current listings and prices for the 51204 across brands and sellers:
Search 51204 bearings on eBay ↗
As an eBay Partner Network affiliate, this site may earn a commission from qualifying purchases made through this link, at no extra cost to you.
FAQ
What bearings are equivalent to a 51204?
The 51204 is built to ISO 104 boundary dimensions 20×40×14 mm by SKF, NSK, FAG, NTN, KOYO, NACHI, Timken, INA. All share the same mounting envelope; match clearance, precision class and (where applicable) seal suffix before substituting.
What are the dimensions of a 51204 bearing?
Bore 20 mm, outer diameter 40 mm, H 14 mm (ISO 104).
Can a 51204 thrust bearing replace a same-size radial bearing?
No. The 51204 is an axial bearing — it carries thrust in one direction only and supports no radial load, so even with the same 20×40×14 mm figures it cannot replace a radial ball bearing. It has a tight-fit shaft washer and a loose-fit housing washer that must not be reversed, needs a minimum axial preload to avoid ball skidding, and a single-direction (51xxx) unit is not interchangeable with a double-direction (52xxx) one.
Related sizes
Boundary-dimension cross-reference only. Per the applicable ISO standard (ISO 15 for ball, ISO 355 for tapered), the boundary dimensions are common across brands, so the mounting envelope is interchangeable. This is NOT a drop-in part equivalence. Internal clearance, precision class, seal/shield type (where applicable), cage material and factory lubrication are encoded in brand-specific suffixes and must be matched separately. Always verify against the manufacturer's catalog before substituting.