The 4 jaw chuck is the most versatile of all the chucks. It can hold round and square shaped materials. Unlike the 3 jaw chuck (self centering) each jaw on the 4 jaw chuck is adjusted independently of the others.Some features of the 4 jaw chuck areHardened steel jaws with stepsReversable range 1/8 to 3 1/4 inchesJaws are independently adjusted in pairsSetting a workpiece off center creates crankcase and cam shapesParts may be machined to run very true (this will require more time to center than a self centering 3 jaw chuck).