A stilson wrench, like the mousetrap, is one of those ingeniously simple inventions that is perfectly designed for a particular task and will never be improved upon. Invented by machinist Daniel Chapman Stilson (1826-1900) of Durham, New Hampshire, the stilson wrench has earned its place as the most popular type of pipe wrench used by plumbers and pipefitters everywhere.

A stilson wrench works by pinching the pipe between two hardened, serrated jaws. The top jaw is connected to the handle by a loose sleeve, which allows the jaws to expand so the wrench can easily slip onto the pipe. Torque applied to the handle squeezes the jaws together. The more pressure that is applied, the tighter the wrench grips.

  Torque here
  pinches jaws
   v      ________________
         |  _   _________ |
---------| |-| |---,    | |
---------|_|-|_|-| |    | |
   Handle         | |    | |
                 | |    | |
                 |_|    |_|
                Lower    Upper
                 Jaw     Jaw

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