Our listings name whirlybirds (roof ventilators) as a use for many of our ball bearings, including the 6203 with a 1/2" bore or 5/8" bore, both 40 mm OD x 12 mm wide, and the 6201 with a 1/2" bore, 32 x 10 mm. There's no single whirlybird size, so match the number or measurements of your old bearing.
Know your bearing's number already? Find it in the table below. If not, the steps further down show how to measure it.
Whirlybird bearing sizes we list
These are the bearings whose listings name whirlybirds, with the sizes exactly as each listing gives them.
| Our bearing | Bore | OD | Width | Seals (as listed) | Pack |
|---|---|---|---|---|---|
| 6203-1/2" | 1/2" (12.7 mm) | 40 mm | 12 mm | 2RS rubber seals | 10 |
| 6203-5/8" | 5/8" (15.9 mm) | 40 mm | 12 mm | 2RS rubber seals | 10 |
| 6203-16 | 16 mm | 40 mm | 12 mm | 2RS rubber seals | 10 |
| 6203-3/4" | 3/4" (19.05 mm) | 40 mm | 12 mm | 2RS rubber seals | 10 |
| 6201-1/2" | 1/2" (12.7 mm) | 32 mm | 10 mm | 2RS rubber seals | 10 |
| 6202-1/2" | 1/2" (12.7 mm) | 35 mm | 11 mm | 2RS rubber seals | 10 |
| 6202-5/8" | 5/8" (15.9 mm) | 35 mm | 11 mm | 2RS rubber seals | 10 |
| 6202-16 | 16 mm | 35 mm | 11 mm | 2RS rubber seals | 10 |
| 6205-2RS-1 | 1" (25.4 mm) | 52 mm | 15 mm | 2RS rubber seals | 10 |
| RLS5-2RS | 5/8" | 1 9/16" | 7/16" | 2RS rubber seals | 10 |
| R8ZZ | 1/2" | 1 1/8" | 5/16" | ZZ shields | 10 |
| 6000 to 6310 2RS | Standard sizes (see the size chart) | 2RS rubber seals | 10 | ||
| 6005 to 6010, 6205 to 6210, 6305 to 6310 2RS, in packs of 2, 3 or 5 | Standard sizes (see the size chart) | 2RS rubber seals | 2, 3 or 5 |
Source: our product listings, checked 12 October 2026. Millimetre values in brackets are the inch sizes converted.
Our listings also name whirlybirds for some small bearings: the 608-RS and 608-ZZ (8 x 22 x 7 mm), the 609-ZZ (9 x 24 x 7 mm), the 606-ZZ (6 x 17 x 6 mm), and a 10-pack range of 604RS to 609RS and 626RS. In bearing makers' tables those last sizes are 604 = 4 x 12 x 4, 605 = 5 x 14 x 5, 606 = 6 x 17 x 6, 607 = 7 x 19 x 6 and 626 = 6 x 19 x 6 mm.
Same outside, different bore: why you measure the bore
Most of the bearings in the table are special bores. They use a standard outer ring with a bore that the standard number doesn't have. The standard sizes are:
| Standard bearing | Bore | OD | Width |
|---|---|---|---|
| 6201 | 12 mm | 32 mm | 10 mm |
| 6202 | 15 mm | 35 mm | 11 mm |
| 6203 | 17 mm | 40 mm | 12 mm |
| 6205 | 25 mm | 52 mm | 15 mm |
Source: bearing makers' published dimension tables (see Sources), the same values as our bearing size chart.
So a whirlybird bearing that measures 40 mm across and 12 mm wide could be a standard 6203 (17 mm bore) or one of our four special-bore 6203s (12.7, 15.9, 16 or 19.05 mm). The outside won't tell you which: only the bore will.
Two catches:
- 16 mm and 5/8" are about 0.1 mm apart. A 5/8" bore is 15.875 mm. Measure the bore to one decimal place, so you can tell 15.9 from 16.0.
- The dash number isn't a standard. Our team's view is that there's no industry standard for these numbers. In our own listings, 6203-8 and 6201-8 are 1/2" bores, 6203-10 and 6202-10 are 5/8", and 6203-12 is 3/4". But -16 means 16 mm on our 6202-16 and 6203-16 and 1" on our 6205 (listed as 6205-2RS-1), and our 6202-1/2" listing also names a 6202-16 among the numbers it replaces. If your old bearing says -16, measure the bore before you order.
How to find your whirlybird bearing size
- Read the number. Look on the side of the old bearing, on the seal or the outer ring, for a number such as 6203. Write down anything after it too (2RS, ZZ, -16, 5/8).
- Measure the bore (the hole) with vernier callipers, to one decimal place.
- Measure the outside diameter across the outer ring, and the width of the outer ring.
- Match all three in the tables above. If nothing matches, use the reverse lookup in our bearing size chart, or send us the three measurements and the number before you order.
- Match the seals. 2RS means rubber seals and ZZ metal shields; the letters don't change the size. Bearing makers rate a contact rubber seal well ahead of a metal shield against water, which counts on a roof. Our seal codes guide explains the letters.
- Count the bearings. We don't list a whirlybird bearing kit: our bearings come in packs (10 for the special bores), so check how many your ventilator takes.
Working on a roof is dangerous. If in doubt, use a roofer. Our bearing listings say all parts need to be fitted by a licensed technician.
Which Bearings Express bearing fits
- Pick the 6203-1/2" bearings if your bearing is 40 x 12 mm outside with a 12.7 mm bore.
- Pick the 6203-5/8" bearings for 40 x 12 mm outside with a 15.9 mm bore.
- Pick the 6203-16 bearings if the bore measures 16.0 mm on the same 40 x 12 mm ring.
- Pick the 6201-1/2" bearings for 32 x 10 mm outside with a 12.7 mm bore.
- Pick the 6202-1/2" bearings for 35 x 11 mm outside with a 12.7 mm bore.
- Pick the 10x 6000 to 6310 2RS if your bearing is a standard number, such as a 6203 with a 17 mm bore.
Every size, including the imperial bores, is in our ball bearings collection.
Questions people also ask
Do you sell a whirlybird bearing kit?
No. We sell the bearings in packs, mostly of 10. Match each bearing in your whirlybird by its number or measurements, and check how many your ventilator takes.
What size bearing is in a whirlybird?
It depends on the ventilator. Our listings name whirlybirds for 6201, 6202, 6203 and 6205 sizes with standard and imperial bores, plus some small bearings. Read the number on your old bearing, or measure it, and match it in the table.
Do you list whirlybird bearings by ventilator brand?
No. Our listings don't name ventilator brands or models, so send us the bearing number or the three measurements and we'll check.
Is a 6203-16 the same as a 6203-5/8"?
No, though they're close. In our listings the 6203-16 has a 16 mm bore and the 6203-5/8" a 15.9 mm bore. Both are 40 mm OD x 12 mm wide.
Related reading
- Bearing size chart 6000 to 6310, with a reverse lookup by measurement
- 2RS vs ZZ bearings: what the seal codes mean
- 608 bearing size: 608ZZ vs 608-2RS
Sources
- NTN, Ball and Roller Bearings, Cat. No. 2203/E: Deep Groove Ball Bearings, dimension tables pp. B-22 to B-25, https://www.ntnglobal.com/en/products/catalog/pdf/2203E_b02.pdf, read 28 September 2026, rechecked 12 October 2026.
- NTN, Ball and Roller Bearings, Cat. No. 2203/E: Miniature and Small Size Ball Bearings, metric series pp. B-48 to B-51, https://www.ntnglobal.com/en/products/catalog/pdf/2203E_b03.pdf, read 12 October 2026.
- NSK, Deep Groove Ball Bearings, dimension tables, https://www.nsk.com/content/dam/nsk/am/en_us/documents/bearings-americas/Deep-Groove-Ball-Bearings.pdf, read 28 September 2026, rechecked 12 October 2026.
- Seal ratings: NTN, Cat. No. 2203/E, Table 1 "Sealed ball bearings: construction and characteristics", p. B-17 (https://www.ntnglobal.com/en/products/catalog/pdf/2203E_b02.pdf), and NSK, Deep Groove Ball Bearings, Table 3 "Comparison of seal / shield performance", p. 5 (NSK URL above), read 2 October 2026.
Checked against bearing makers' dimension tables and Bearings Express product listings on 12 October 2026.
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