When slipped on the end of a crankshaft, these specially designed sockets let you use a 1/2" drive ratchet or breaker bar to rotate the engine assembly. Our sockets also have the unique feature of a provision to hold our degree wheels or any wheel with a 1" or larger center hole. The knurled retaining nut actually sandwiches the degree wheel and holds it in place. This can then be loosened while on the crank snout so that you can turn the degree wheel independent of the engine, which is really handy when finding TDC.