A general purpose wrench that can be adjusted to a wide range of sizes. This kind of wrench can be useful for turning large nuts under low pressure when you do not have the appropriate socket (for example, the plastic oil filter cap on some vehicles).

To operate, pull the handles fully apart, slide the bolt in the middle into the correct position and close the handles again. The nut is shaped so that it cannot slide when in normal use, so the position should remain unless you open the handles all the way.