GBD Silicon Carbide Type. Heavy Duty Block Cylinders. With minimal stock removal and without damaging or changing the micro substructure of the metal, the Flex-Hone tool plateaus the surface, removes cut, torn and folded metal creating a cross-hatched finish that retains a film of oil, reducing friction, ring wear, and the factors that lead to scuffing. In hydraulics and two-stroke engines there is the double benefit of radiusing the ports and finishing the cylinder walls in a single operation.