Self-centering and independent chucks are tools used in metalworking to hold and center workpieces on a lathe. Self-centering chucks are usually equipped with three jaws and are often used for series production. The chuck is actuated by turning a central thread, which causes the three jaws to simultaneously center on and hold the workpiece. Self-centering chucks are quick and easy to operate because they automatically center and hold the workpiece. Independent chucks can have two, three or four independent jaws, each of which can be adjusted separately to hold the workpiece. Independent chucks are usually for single pieces or small batches and require manual adjustment of the jaws. This requires more time and skill than self-centering chucks, but offers greater flexibility and precision. The choice between a self-centering and an independent chuck depends on several factors, such as the number of workpieces to be machined, the size and shape of the workpieces, the accuracy required, and the time available to adjust the chuck.