Slip joint pliers, also known as adjustable pliers, are hand tools which are used for clamping down on objects for tightening and loosening purposes, or for bending the object being gripped. Originally called "channel locks," slip joint pliers were invented by engineer Howard Manning in 1933. Manning was an employee of the Champion-DeArment Tool Company, and his channel locks proved to be so popular that thirty years later in 1963, the company changed its name to Channellocks, Inc. to take advantage of the tool's name recognition.
The teeth of slip joint pliers are jagged or toothed to increase gripping ability for a wide variety of object sizes and shapes. To further accommodate varying object sizes, slip joint pliers have an adjustable jaw. The jaw of a straight slip joint plier type of plier has a setting for clamping down on smaller objects and a setting for clamping down on larger ones. Straight slip joint pliers possess jaws which are lined up with the handles of the pliers. One side of a pair of two straight slip joint pliers has a short slot through which a pivot point or fulcrum can move. To widen or narrow the opening of a pair of slip joint pliers with a straight slip joint plier, the user must fully open the pliers and move the handle with the slit along its pivot. When the desired opening width has been obtained, the handles are closed to secure the positioning.
Another type of slip joint plier is the tongue and groove, which was the original channel lock design created by Howard Manning. They are also known as groove joint pliers and adjustable pliers. The tongue and groove slip joint plier features jaws which are not aligned with their handles, instead sitting at a 45 or 60 degree angel from the handles. The lower jaw is capable of multiple position adjustments by way of a notched track or slit in the handle of the upper jaw. Adjusting the jaw size of a tongue and groove slip joint plier has no effect on the distance between the handles. The handles are often quite long, ranging in length from nine inches to over a foot. The long handles are intended to provide the user increased leverage when tightening, loosening or bending an object. Handles on tongue and groove slip joint pliers are frequently coated in rubber to enhance gripping ability, thus further increasing the force and stability of the leverage being applied to the object.
Both types of slip joint pliers are most commonly used for loosening and tightening nuts and bolts. They can also be used to pull nails, though in this capacity they are somewhat less effective than the claw end of a hammer. There are a variety of slip joint plier sizes, from as small as four inches to as large as twenty inches, but the model most commonly found in the average homeowner's toolbox is six inches in length.