A machine tool arbor for holding a rotating machine part or workpiece is fitted with an actuator member at a back or distal end of an arbor main body for tool-less chucking and unchucking of a machine part or workpiece at a front or proximate end of the arbor main body. An actuator ring or knob is mounted at the back end of the arbor main body which, when rotated in one direction, causes an pusher member (collet pusher part, hydraulic piston) to move in such a manner as to displace a chuck member (inclined collet, flex collet, expansion ring) and release the machine part or workpiece that is chucked. When rotated in the opposite direction, the actuator knob causes the actuator member to move in an opposite manner as to fix the chuck member in a position to firmly hold the machine part or workpiece to be chucked. With this fitting, the machine part or workpiece can be chucked and unchucked by convenient operation of the actuator knob at the back end of the arbor without the need for using a special chucking tool.