tongue and groove pliers
Tongue and groove pliers are pliers with serrated teeth that grip flat, square, round, or hexagonal objects. The jaws can be set in up to five positions by slipping the curved ridge into the desired groove. Large tongue-and-groove pliers are often used to hold pipes because the longer handles give more leverage. The jaws stay parallel and give a better grip than slip-joint pliers.
Using tongue and groove plier invovles a simple procedure. With pliers open to the widest position, place the jaws on the object to be held. Decide which groove gives the best position. Squeeze the handles until the pliers grip the object.