Thrust bearing sizes: the 51100 and 51200 series chart, and which washer goes on the shaft

A thrust bearing takes load along the shaft (axial load), not across it, and the smallest in the standard 511 series, the 51100, is 10 mm bore x 24 mm outside diameter x 9 mm high. The 51200 series is bigger for the same bore. We sell 51100 to 51110 thrust bearings and 51201 to 51212 in packs of 2.

If you know your number, find it in the table below and you can stop there.

51100 and 51200 thrust bearing size chart (mm)

Source: bearing makers' published thrust bearing tables (see Sources), read 30 September 2026, cross-checked between two catalogues: all 23 rows agree. D1 is the smallest the housing washer bore can be. The 23 sizes are the ones we list (our product listings, 30 September 2026).

Which washer goes on the shaft?

A 51100 or 51200 bearing comes apart into three pieces: two flat washers (the shaft and housing raceway washers) and the balls in their cage between them. The washers are the same outside size, so they're easy to mix up.

The difference is the bore. The shaft washer has the smaller bore, the same as the bearing number's bore. The housing washer's bore is 1 to 2 mm bigger, so it clears the shaft and sits against the housing. On a 51106 the shaft washer is 30 mm and the housing washer is at least 32 mm. Put the bigger-bore washer on the shaft and it's a loose fit on a 30 mm shaft.

Three more things the makers say about these bearings:

• Axial load only, in one direction. It can't take radial loads, so something else has to carry the side load.
• Keep some axial load on it. A thrust bearing needs an axial load to stop the balls slipping on the raceways.
• Not for high speed. Single direction thrust ball bearings aren't suitable for high speed operation.

51100 or 51200: which series do I need?

For the same bore, a 512 bearing has a bigger outside diameter, is taller and carries more load than a 511. At 30 mm bore, a 51106 is 47 x 11 mm and a 51206 is 52 x 16 mm.

In practice, match the old bearing, since the housing space decides it. These pairs share an outside diameter:

• 28 mm OD: 51102 (15 mm bore, 9 high) or 51201 (12 mm bore, 11 high).
• 35 mm OD: 51104 (20 mm bore, 10 high) or 51203 (17 mm bore, 12 high).
• 47 mm OD: 51106 (30 mm bore, 11 high) or 51205 (25 mm bore, 15 high).
• 52 mm OD: 51107 (35 mm bore, 12 high) or 51206 (30 mm bore, 16 high).

How to read a thrust bearing number

Take 51206 as the example.

1. 5 is the type: a single direction thrust ball bearing.
2. 1 is the height series.
3. 2 is the diameter series. A 2 has a bigger outside diameter than a 1 for the same bore, which is the 51100 vs 51200 difference.
4. 06 is the bore code: 00 = 10 mm, 01 = 12, 02 = 15, 03 = 17. From 04 up, multiply by 5, so 06 = 30 mm and 11 = 55 mm.

It's the same bore code as a deep groove ball bearing, so a 51206 and a 6206 both fit a 30 mm shaft.

How to measure an old thrust bearing

1. Separate the three pieces and find the washer with the smaller bore. That's the shaft washer.
2. Measure its bore with vernier callipers. That's the d column.
3. Measure the outside diameter of either washer.
4. Stack the three pieces back together and measure the total height.
5. Find the matching row in the chart. If only the OD matches, check the pairs above.

Which BES product fits

• Pick the 2x 51100 to 51110 thrust ball bearings for a 10 to 50 mm shaft in the lighter 511 series. Choose the size from the drop-down.
• Pick the 2x 51201 to 51212 thrust ball bearings for a 12 to 60 mm shaft where the old bearing is a 512. The 512 series is the heavier one, but it only fits if the housing has room for its bigger OD and height. We don't list the 51200 (10 mm bore).

Both thrust listings are in thrust bearings.

Replacing the clutch thrust bearing on a Greenfield mower (part GT0393)? That one isn't a thrust ball bearing. It's a sealed 6206-2RS deep groove ball bearing, 30 x 62 x 16 mm, and it doesn't swap with a 51206 even though both have a 30 mm bore. We sell it as the bearing for the Greenfield GT0393 clutch thrust bearing.

Questions people also ask

What size is a 51211 thrust bearing?

A 51211 is 55 mm bore x 90 mm outside diameter x 25 mm high. Its housing washer bore is 57 mm.

What is a 10mm thrust bearing?

A 51100: 10 mm bore x 24 mm OD x 9 mm high. The heavier 51200 is 10 x 26 x 11 mm, but we don't list it.

Is an axial bearing the same as a thrust bearing?

Yes. Axial means along the shaft, and a thrust ball bearing is built for axial load. It carries axial loads but no radial loads.

Can you get a sealed thrust bearing?

Not in these series from the makers we checked. Their 511 and 512 tables list open bearings only, with no seal or shield versions.

What are the 51110 thrust bearing dimensions?

50 mm bore x 70 mm OD x 14 mm high. The 51210 has the same 50 mm bore but is 78 mm OD and 22 mm high.

Related reading

• Bearing size chart 6000 to 6310, which uses the same bore codes
• UCP204, UCP205 and UCP206 pillow block dimensions

Sources

• NTN, Ball and Roller Bearings, Cat. No. 2203/E: Thrust Bearings, pp. B-253 to B-257 (ntnglobal.com/en/products/catalog/pdf/2203E_b09.pdf), read 30 September 2026.
• NTN, Ball and Roller Bearings, Cat. No. 2203/E: Boundary Dimensions and Bearing Number Codes, Table 5.2, p. A-50 (ntnglobal.com/en/products/catalog/pdf/2203E_a05.pdf), read 30 September 2026.
• NSK, Rolling Bearings for Industrial Machinery, CAT. No. E1103, Part C, Thrust Ball Bearings, pp. C 296 to C 301 (nsk.com/common/data/ctrgPdf/bearings/nsk_cat_e1103b_partc.pdf), read 30 September 2026.

Checked against the NTN and NSK catalogues and our product listings on 30 September 2026.