Fits Mustang 4.6L and 5.4L 3V engines with 12mm spark plugs. Does not fit 3V heads with "High Thread" design spark plugs. Required when installing Ford Performance headsM-6049-463VP3 ,M-6049-N3V ,M-6049-N3VPA andM-6050-463VP3 ,M-6050-N3V ,M-6050-N3VPA on 2005-2007 and early 2008 Mustang GT originally equipped with "High Thread" design heads.
