I've had several of the Ruger Mark IV pistols cross my bench since they were first issued. I was really taken aback when I had several of these pistols apart. The part that especially made me wonder about what the heck they're doing involves the safety detent: The steel detent on the left has been used since the very first Ruger Standard was made in 1949, the black plastic detent began being factory installed in the Ruger Mark IV pistols. Check out the working end of the black plastic detent from a Ruger Mark IV safety. The working end has now worn flat from moving the safety from "ON to OFF", and not very many times. Needless to write that I've replaced the one in my pistol!