Originally Posted by Davidka

You can flip them over, both sides are usable. Make sure the diff is smooth after you flip the rings, clean everything re-lube and reassemble. If a diff is allowed to slip too much, the balls can be damaged too. If they're not good, it's no use to run it until you have new balls and rings (smc sells carbide balls qty. 50, $12). Diff rings are cheap so it's not a bad idea to keep an extra set on hand.