a wire helix 52 both of which are generally parallel to the bolt axis 42 paddles 54 extending downward from the bolt 20 flank the left and right side of the wire helix 52 and receive a transversely extending metal bar 56 passing through corresponding holes 58 in each of the paddles 54 to intersect the wire helix 52 and to be held captive by its coils the paddles 54 and bar 56 provide a helix follower that moves along the axis 42 with rotation of the wire helix 52 the wire helix 52 is preferably a spiral of spring tempered stainless steel wire following a three dimensional curve that lies on a cylinder of a defined diameter and having a central axis parallel to axis 42 the wire of the wire helix 52 will have a defined angle with respect to a plane perpendicular to the axis 42 termed its lead angle the lead angle may be controlled simply by spacing between wire coils along the axis of the wire helix 52 referring now to fig5 the wire helix 52 provides a number of different pitches and diameters and thus different lead angles where lead angle 65 as described above is the angle between a plane orthogonal to the axis 42 and the wire of the helix 52 for a given helix diameter the lead.