A tool or workpiece has a mounting collar open axially outward, formed with a radially inwardly directed angled flank, and having a radial outer surface of noncircular cross-sectional shape. A chuck has a body formed with an axially forwardly open socket shaped to receive the collar with the axes generally coaxial and having an inner surface of a noncircular cross-sectional shape substantially complementary to the shape of the collar outer surface. A plurality of jaws axially fixed in the socket have radially movable ends engageable inside the collar and each formed with a radially inwardly and axially outwardly directed face. A cam having a face centered on the axis is engageable with the jaw front ends such that axial rearward shifting of the cam presses the jaw front ends outward and thereby presses the jaw faces against the collar flank to lock the collar in the socket.