Goodson's Diamond Valve Guide Flex-Hones combines the flexibility of a Flex-Hone with the speed of a diamond. These 400 grit Flex-Hones are made with highly friable resin bond diamond crystals for the more demanding finish requirements of hard materials. Applications include: Heat treated steel, High nickel stainless steel, Chromed or plated bores, MMX aluminum alloys, and Ceramic & Carbide.