# Miniature Ball Bearing Sizes

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…