A pipecutter is a tool used by plumbers to cut pipe. It is effectively a vise with a blade on it. A knob tightens the vise around the tubing, bringing the blade into contact with it. Once contact is made, the pipe-cutter is spun around on the tubing causing the blade digs into the tubing and eventually sever it.
Besides producing a clean cut, a pipecutter is often a faster and more convenient way of cutting pipe than using a hacksaw. On the other, hacksaws will cut nearly any size pipe made out of most metals and plastics, whereas pipecutters are more limited.
Plastic tubing cutters, which resemble pruning shears, may be used for thinner pipes and tubes such as a sprinkler pipe.