18mm (.709") Flex-Hone Cylinder Hone Tool 240 Grit (Silicon Carbide) Flexible Cylinder Hone made of Silicon Carbide Hone is Made in USA by Brush Research Manufacturing Hone is self centering and can be used with 3/8" or 1/2" chuck drill Perfect for bore honing and cylinder refinishing The hone size listed on the product is the bore it is intended to be used for (or slightly smaller bore will work)