The 5" back up pads with a central locating button are designed for use with 125mm surface conditioning discs.
SCM discs are supplied with a 10mm centre hole which allows for simple location on the back up pad. The location pin eleiminates disc vibration and improves surface conditioning disc life as well as reducing back up pad wear.
For centralising surface conditioning discs on 125mm / 5" angle grinders
125mm x 10mm back up pad with location pin - M14 thread
For 5" / 125mm angle grinders