A handy gauge for checking shells for proper size. Tests roundness and outside diameter of the brass. If shell is too large for the "go" hole, it needs resizing. If shell slips easily into the "no go" hole, it has been sized down too far and will reduce the life of the brass. A must for adjusting the collets on Grabber, Hustler, SizeMaster and Super-Saver. Tests 10, 12, 16, 20, 28 and .410 gauges.