Schaller M4S is the tuner, and yes, the capstan/pinion of a Grover Titan will fit in a Schaller M4S. I know this because I had an M4S with a broken central screw in my Victory Artist and I replaced the capstan/pinion/screw with one from a Grover Titan. Worked fine. Eventually I got the right bits from Schaller to fix it though.