This is the ring the connects to the bottom of the stylus arm. It is 12mm (.48") thick, 38mm (1.52") diameter, and made of Teflon. Used to avoid scratching sheet metal, but it wears down faster than Brass (M011B0) or Steel (M011S0)
M015S0 Pictured
Attached with HWM9X5T screws
Mazak® Part # 46572301041 T.