Having had to look up ball bearing sizes far too often, here’s the table…
| Bearing | ID | OD | Thick |
| 603 | 3 | 9 | 5 |
| 623 | 3 | 10 | 4 |
| 633 | 3 | 13 | 5 |
| 683 | 3 | 7 | 3 |
| 693 | 3 | 8 | 4 |
| 605 | 5 | 14 | 5 |
| 625 | 5 | 16 | 5 |
| 635 | 5 | 19 | 6 |
| 606 | 6 | 17 | 6 |
| 626 | 6 | 19 | 6 |
| 608 | 8 | 22 | 7 |
| 629 | 9 | 26 | 8 |
The first digit is something like the bearing type; I think 6xx = miniature bearings.
The second digit has something to do with the overall size, but is a code rather than an actual dimension.
The last digit is, hal-lay-loo-ya, the actual bore diameter.
[Update: Shows what I know; an excellent explanation of the numbers lives there. The short summary:
- First digit: bearing type, 6 = single row deep groove
- Second digit: series, 0 = extra light, 2 = light, 3 = medium duty, 8 & 9 = thinner
- If three digits, third digit = ID in mm
- If four digits, last two = ID/5, except 00-03 = 10/12/15/17
Moral: always verify everything you read on the InterTubes!]
Of course, a randomly chosen eBay listing will list the bearing size as:
- ID x thickness x OD
- OD x thickness x ID
- ID x OD x thickness
- and be wrong in at least one dimension
Of most interest to Thing-O-Matic hackers: a 635 bearing ought to fit a NEMA 17 stepper shaft (pay attention if you’re buying surplus: not all are 5 mm) and slip into the same hole as a 626 bearing.
Alas, there seems to be no 5 mm ID bearing equivalent to the 606 bearing in the MK5 extruder head, but a 0.5 mm = 20 mil shim around the outside would adapt a 625 to that hole. Might take some careful forming, though.
Buy ’em in bulk and save…
The Smell of Molten Projects in the Morning 