Three-jaw chucks, of the same general type used to hold bits in most power drills, are also common equipment on metalworking lathes. Though it is not necessarily so, three-jaw chucks are so commonly of the self-centering variety, in which the jaws are not independently adjustable, that “self-centering” is generally assumed from the term “three-jaw chuck.”
But there are distinct advantages to using a four-jaw chuck (which is generally assumed, contrariwise, to have independently-adjustable jaws), and though a three-jaw chuck is nice to have for convenience and for use with hexagonal stock, most machinists find the four-jaw chuck to be more versatile and useful in the long term.
This table is adapted from a list by Bruce Simpson, as quoted on Frank Hoose’s excellent lathe-work site.
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