I've already discovered that using the closest standard-sized axles, 3/16" = 4.763mm, are too small for 5mm I.D. bearings, even only a quarter of a millimeter is too much play.
So, other than filing or grinding the 3/8" aluminum wheel bearing holes a bit wider to accept the 10mm bearing, and keeping the 5mm axles, is there anything you can do with a 5 x 9mm bearing to make it just big enough to snugly fit inside the 3/8" hole? Of course, I've never seen a bearing that has metric 5mm I.D. and SAE 3/8" O.D. or else I'd buy some.
