The anti-rotation rod 60 is a generally thin, elongated member having a cross-section complementary to the cross-section of the insert bore 58 and adapted for non-rotational slidable register with the insert bore 58. (The anti-rotation rod 60 is omitted in FIG. 3 for clarity.) The rod insert 56 is typically machined from a material, such as brass or bronze, that minimizes wear on the anti-rotation