Four-jaw chucks have four advantages over three-jaw chucks. (1) They can be used to hold irregularly shaped parts. (2) With the use of a dial indicator, they can be used to center parts with a great deal of accuracy. (3) Four-jaw chucks can be used to deliberately hold a part off-center. (4) They can clamp stock tighter. This is a valuable asset when machining cams, crankshafts, and similar parts. The main disadvantage of the 4-jaw independent chuck is that the jaws must be individually set, adding considerable time to setups. A hex key (provided) is used to tighten each jaw individually. Tommy bars (also provided) are used in the holes in the side to tighten and loosen the chuck for more leverage. A groove is provided around the base of the chuck so that angle clamps can be used to mount it to the table of a mill as a holding fixture.