Replacement of the pin is for the factory to do in all cases. Less invasive measures are called for in all other cases where the building factory is not involved. As mentioned in other posts, the pin is usually not worn enough to replace, is ridiculously expensive to file and reengrave, and the new pin will not properly engage the surfaces of the hook. Many pins are not one piece and hardly anyone understands Model 21 or Parker pin construction, even if they claim to. My friend Joe Wood made the best case for not messing with the pin. In 99 out of 100 cases, even a talented smith will ruin the gun. The new pin will show up like a turd on a collard leaf.