Abstract

A chuck centered on an axis and having a plurality of jaws each displaceable radially of the chuck axis is usable in combination with a drill bit having a shank formed with respective grooves each having axially extending and angularly directed flank surfaces engageable with the jaws to rotationally link the bit to the chuck. Each jaw is substantially symmetrical to a respective jaw plane extending substantially radially of the chuck axis. In addition each jaw is formed with a pair of angularly spaced teeth substantially symmetrically flanking the respective jaw plane and each having a respective inwardly directed edge and an outer tooth surface extending radially back therefrom and angularly away from the respective jaw plane. Each jaw also has pair of angularly spaced shoulder surfaces substantially symmetrically flanking the respective outer teeth surfaces and each having an inner end generally tangent to an inner plane substantially perpendicular to the respective jaw plane and parallel to the chuck axis and an outer end generally tangent to an abutment plane extending substantially parallel to the chuck axis and at an angle to the respective jaw plane corresponding to the angle formed by the respective bit-shank flank surface at the point of contact with the respective shoulder surface, the inner plane lying radially outward of the respective teeth edges.