[ItBites]

NG,

Did you really mean out-of-round in Drum Brakes?

If so, you would use a dial gage or dovetail to measure out of round. Chuck the drum in the brake lathe using the correct collars to center the drum on the hub. Then spin the drum by hand while a dovetail or dial caliper rests against the friction surface. Out-of-round (more correctly "run-out") will show up as variation in the reading as the drum is turned.

Hope this actually answers the question you intended to ask...