The quick-release chuck is the part of the drill located at the end of the drill that is used to hold work tools such as drill bits or bits firmly in place. The "quick-release" designation means that no additional wrench or other tools are needed to change the tool. The chuck usually consists of two pivoting parts. By holding one part and turning the other, the inner jaws are contracted or expanded to clamp the tool firmly. This is a more convenient system compared to the older crank chucks where a special toothed wrench was required for each tightening. In addition, some quick-release chucks are equipped with a so-called locking lock, which is indicated by an audible click on final tightening. This click signals that the tool is securely and firmly locked against slipping during work.