rock pads need a 30/50 degree angle when it comes to a grind ....no need to press mega hard medium grind is fine......i have used stone discs and metal cuting discs ....im using a 2.5mm cutting disc and it gives me a beastly grind......always remember u need to brush the rim fast........ and benito and carlse both use stone cutting discs 4mm wide 70 degree angle