[LazyPup]

You are correct, you do not rotate a cast iron snap cutter.

The snap cutter chain is wrapped around the pipe at the point of the desired cut then connected back to the cutter head in the same manner as attaching a chain wrench.

On the inside of the chain there are a series of small cutter points or teeth. As the chain is tightened by the crank the points create a series of stress points around the pipe. Cast iron is a very brittle metal and as the chain stress increases it will reach a point where you will hear a distinct snap. When you hear the snap remove the wrench and you will see a clean fracture line completely around the pipe.