Valve seat COUNTERBORE POCKET CUTTER range: 1 5/8″ – 1 7/8″(41.27 – 47.62mm). To be used with 3/8 top pilots, blades included. These cutters are to be driven by a powered machine, very practical to cut out a seat to be replace, carbide blades will cut hard seats out, very handy to clean out an aluminum seat pocket after welding, head body made out of anodized aluminum, carbide blades. “Cam lock” holding screw.