Locking pliers are pliers which are designed to be locked closed, holding an object firmly without the need for the grip of a human hand. There are a number of different styles of locking pliers designed for various applications, and this product is readily available from many hardware stores. It is also possible to special order a set of pliers from a manufacturer or specialty company for a particular purpose.
One popular brand of locking pliers is Vise-Grip®. As a general rule, no matter what the brand, these pliers typically have a screw which is used to adjust the pliers to the desired width apart, and a release handle which can be used to force the pliers open when they are no longer needed. When the pliers are locked down, they will hold onto the object without requiring the operator to grip the handles. This can be tremendously useful for all sorts of applications.
In some cases, a pair of locking pliers can act like a second set of hands, stabilizing an object and holding it in place while it is being worked on. These pliers can also be used to hold an object which could not be held by hand, such as something which is being welded. Locking pliers can also be used to loosen stubborn bolts and other fixed objects; it's easier to lock the pliers into place and turn them than it would be to maintain tension on a pair of pliers while simultaneously trying to turn them to loosen the object in question.
The quality of a pair of pliers can vary considerably. If cheap metals are used, the pliers may develop metal fatigue and fail, and they could also tarnish or rust over the course of use. Poor designs can make pliers subject to mechanical failure; for example, the screw used to control the width of the pliers could snap off, or the release could break, making it difficult to remove the pliers.
A pair of locking pliers benefits from some routine maintenance and care. It is a good idea to periodically wipe down the pliers and oil the moving parts so that they will move freely, and to avoid keeping pliers in moist or corrosive environments. In the case of a tool like needle-nose locking pliers, it is also a good idea to store the pliers in an environment where they will not be bent or twisted, as this can impede their usefulness.