MR bearing sizes: a guide to MR miniature bearings
MR bearings are thin miniature ball bearings, and their numbers hide the size in plain sight. Here is how to read them, with a size table from MR84 to MR128.
MR bearings are thin miniature ball bearings with metric sizes. They turn up in RC models and drones, fishing reels, 3D printers, small motors, dental handpieces and instruments. The numbers look random at first, but once you know the pattern you can read the size straight off the part number.
How to read an MR number
After the letters MR, the digits give the outside diameter first, then the bore, both in millimetres:
- MR93: 9 mm outside diameter, 3 mm bore.
- MR106: 10 mm outside diameter, 6 mm bore.
- MR128: 12 mm outside diameter, 8 mm bore.
This is the opposite of most bearing numbers, where the last digits describe the bore. The width is not in the number at all, so you need a table, or a caliper, for that.
MR bearing size table
| Part number | Bore (mm) | Outside diameter (mm) | Width, shielded ZZ (mm) | Width, open (mm) |
|---|---|---|---|---|
| MR84ZZ | 4 | 8 | 3 | 2 |
| MR85ZZ | 5 | 8 | 2.5 | 2 |
| MR93ZZ | 3 | 9 | 4 | 2.5 |
| MR106ZZ | 6 | 10 | 3 | 2.5 |
| MR126ZZ | 6 | 12 | 4 | 3 |
| MR128 | 8 | 12 | 3.5 | 2.5 |
All of these are available – ask for stock, in multiple brands.
Why open and shielded widths differ
In many miniature sizes the shielded (ZZ) or sealed (2RS) version is wider than the open one, because the shields need room. An MR93ZZ is 4 mm wide, but an open MR93 is only 2.5 mm. If you measure an old bearing, check whether it had shields, and quote the width you actually measured. A difference of 1.5 mm is easily the difference between a part that fits and one that does not.
Variations you will see
- ZZ: metal shields on both sides. 2RS: rubber seals on both sides. No letters: open. See ZZ or 2RS?
- FMR: the flanged version, with a lip on the outer ring, such as FMR106ZZ. Read flanged bearings explained.
- S or SS in front: stainless steel, for wet or corrosive conditions.
- Z3V3 on the box: a low-noise grade, not a size. Read what Z3V3 means.
MR or 6xx?
The other common family of miniature bearings uses three-digit numbers such as 604, 623 and 686, where the last digit is the bore. Our bearing size chart lists both families side by side, and the miniature bearings page has more common sizes.
Measuring a miniature bearing
Use a digital caliper that reads to 0.1 mm. Miniature sizes are often half-millimetre values such as 2.5 or 3.5 mm, and a ruler cannot tell them apart. Wipe off grease, take each reading two or three times, and send us bore × outside diameter × width. Our guide on how to measure a bearing shows how.
Need an MR bearing?
Send us the number or the three measurements on WhatsApp, with the quantity. We supply single pieces for repairs and larger quantities for manufacturers, across India, with same or next-day delivery in Mumbai.