Flex-Hone tools create a cross-hatch finish on the ID of the valve guide bore for better oil retention and less wear on both the valve guide and the valve stem. The BC Series Flex-Hone tool is designed for use on any type or size of cylinder from 4mm up to 3" in diameter. This cylinder hone is designed for surface finishing and cross hole deburring in brake cylinders, wheel cylinders, hydraulics, pneumatics and valve guides.