re cheap balls - I guess chinese balls will always be a bit smaller than imperial ones ;-) ... But 4mm is a huge difference. The closest metric size would be 6mm. If one were to use 20 x 4mm balls in a WM20 race, there would be 40mm spare space or 1 5/8" That seems difficult to miss.
I can vouch for Trevor's method of removing difficult races. I took two out of a JCB that were impossible to move. The ring of weld as it cools contracts the race.
"Arc Welders, so much more than just a cutting torch!"
