Talked to White's today and the metal coil mounting screw was changed about six years ago to fiberglass reinforced nylon. Current machines no longer use metal screws. The metal screw does show up in test and causes a slight north to south mushy needle response as compared to east to west during pinpointing. I though something seemed different! The older machines were set to null out the screw with as little loss possible. If you have an older 6000 di pro and purchase a new coil, it will require a coil adapter kit that they will supply for free. I think I am going to upgrade to the new style lower shaft and nylon screw and forget about converting new coils to fit a metal screw type shaft. For those having the older machines, this might be a sensible update. Warning: you can get different stories from White's depending on who you talk to.