One of the meanings of the word wrench is any of various hand or power tools, often having fixed or adjustable jaws, used for gripping, turning, or twisting objects such as nuts, bolts, or pipes.
Plumber wrench is a tool to screw (rotate with force) various pipes during plumbing. The diameter of the pipe being screwed is adjusted by rotating the key ring. This tool can deliver significant force (by inaccurate work it is possible to break the pipe) and thus does not need to engage a nut. However, the tool can still be used on a pipe with a nut or other flat engagement points when such surfaces are available. Being relatively large and unwieldy, this tool is only used when the ordinary wrenches are not suitable.