The PS-8503-00 is the blank version of the PS-8501-00 String Saver Saddles (you make the string slots and determine the string spacing) to upgrade or replace the existing saddles on your Gibson Nashville Tune-o-matic bridge dated after 2000. These are also the saddles we load into our ResoMax NV2 Bridges and They are a drop in replacement on tune-o-matic bridges with API stamped on the bottom! String Saver Original saddles are made with a unique combination of materials made to enhance tone and dramatically reduce string breakage. Each saddle is impregnated with PTFE, the slipperiest substance on earth. The PTFE in String Savers eases the grip between the saddle and string, spreading the stress over a greater portion of the string, just enough to drastically reduce string breakage.