Valve Seat Cutter, Seat Cutter 1.680" Seat OD .630 Guide, Spring Seat Cutter - 1.680" Spring Seat O.D., .630 Guide O.D., None, This valve seat cutter allows you to enlarge the cylinder head spring pocket to 1.680" outer diameter while reducing the outer diameter of the valve guide to .630"., Engine Valve Seat Cutter