Abstract: A shaft clamping device is disclosed comprising an annular collar having a radial through slot. The collar has a recess and a coaxially aligned tapped opening respectively formed on opposite sides of the slot and which cooperate with a clamping screw for expanding or contracting the diameter of a clamping surface defined by the center opening of the collar. The collar recess includes a tapered diameter surface between an enlarged entrance of the recess and a clearance hole therein to provide a clamping screw bearing shoulder for seating a tapered diameter bearing surface of the clamping screw and providing for reduced stress concentration in a clamping collar of increased strength.