Abstract: An adjustable collet is provided comprising a step collet, a plurality of machinable and removable jaws, and means for interlocking the jaws with the step collet. The interlocking means comprise counter-bored and threaded holes spaced on the face of the collet, and hollow bosses projecting from one surface of the jaws and aligned with counter-bored or counter-sunk holes on the opposite surface, the interlocking means being effected by mating the jaw bosses with the holes in the collet face and by engaging screws passing through the holes and bosses in the jaws to the threaded holes in the collet face. To further increase the capacity of the collet, extension bars are utilized that incorporate the above-described interlocking means.