US Patent 7938046 Torque-limiting device

A torque-limiting driver has a handle, a body, a torque-limiting assembly and a work-piece engaging tip. The torque-limiting assembly includes an upper and lower shank that have a plurality of teeth circumferentially spaced. The teeth have a vertical face, an inclined face and a flat peak. The inclined face is defined by a radius of curvature that transitions to the flat peak. There is a spring for applying pressure across the upper and lower shank. The teeth engage for relative rotation when the handle is turned and disengage when a predetermined value of torque is exceeded.