What size socket do I need to change out spark plugs? For the majority of plugs, you need a 5/8 or 16mm socket. Some Fords use 9/16″ plugs, some newer European and Asian vehicles use 14mm plugs, and there are a few applications that use 7/8″, 13/16″, ¾” or 18mm plugs. All spark plugs are 6 sided, except some BMW engines. These plugs must be removed with a thin wall 12 point 14mm socket. Spark plug sockets have a magnet or a rubber sleeve that grips the plug, helping you pull it out of the head. If you dont have one handy, you can loosen the plug with a deep well socket, then use a magnet to lift the plug out of the plug well.
