The 7" back up pads with a central locating button are designed for use with 178mm 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 180mm / 7" angle grinders
Back up pad with 10mm location pin
178mm, M14 thread