Nipple wrench (plumbing)
In plumbing, a nipple wrench is often known as an inside pipe wrench.
An eccentric toothed gear is mounted on a hexagonal shaft. The wrench is introduced inside the pipe. As the wrench is turned, the eccentric gear is forced to grip the inside of the pipe. As with a regular pipe wrench, the mechanism is such that the grip on the pipe increases with the torque applied on the wrench.
It is a relatively obscure but often useful tool.
