a rotatable driving tool for imparting torque to a driven member , such as a threaded fastener having an axial recess in the head thereof , comprises a circularly cylindrical body with a plurality of substantially circularly helical driving portions projecting laterally therefrom and equiangularly spaced about the cylindrical axis , each of the driving portions having a small helix angle , preferably between one and three degress . the driving portions mate with lobes of the fastener recess but are slightly inclined with respect thereto to provide a wedge fit to retain the fastener in engagement with the tool body .