A driver tool for insertion and removal of a first part configured for threaded engagement in a corresponding threaded bore in a second part has a driving end portion of polygonal shape with multiple flats configured for engagement in a recess in the first part having a corresponding polygonal shape. Some or all of the flats have a respective grabbing feature or edge designed to grab or grip into the opposing surface of the recess to allow a greater amount of torque to be applied to the first part when the tool is rotated in the unthreading direction than when it is rotated in the opposite threading or insertion direction.
