prevent the steel flange from bearing directly against the wheel and tending to crack it; trained workers are expected to know and obey this rule. Thus the entire contact area between flange and wheel is covered, either with paper or with compressible coating (rubber or gasket) on the flange. The wheel's inner diameter may meet the arbor precisely or may be larger with a bushing (sleeve) to reduce it. Before the new wheel is mounted it is ring tested, which involves gently tapping it with a fingernail or tool handle (wood or plastic) to hear its high-pitched ring (comparable to a bell's ring, although not loud), indicating that it is not cracked. It is rung in various spots to be sure. A "flat" or "hoarse" sound (failing to "sing") indicates a crack. With the wheel having passed the ring test, the bushing (if any), wheel, paper blotters, steel flanges, and nut are assembled, and the nut is tightened, not as hard as possible, but enough to be firmly fastened in place. The guard is reinstalled, and then the grinder can be plugged in again. Dressing may be needed afterward. When the wheel is first started, the operator stands a bit off center, so that if it were to explode, less pathway for injury exists. References Bibliography Grinding machines