Designed for spark plug size: M14 x 1.25mm with flat sealing area. Milling head diameter 20mm . Cleaning of the spark plug seat using a compression spring with integrated flat seal seat milling tool. Manufactured from chrome molybdenum for long life. The 13mm drive hex is equipped with a spring-loaded detent ball to help hold the assembly in the socket. Length of tool 55mm NOTE: do not use on tapered spark plug seats.