This unique and patented design works on 2004-newer Ford F150 pickup trucks with 5.4L 3-valve Triton V-8 engines.  Socket end is 9/16”.  Soft rubber insert holds and protects spark plug during removal and installation.  Extension is part of the socket.  Easily fits down spark plug tube in cylinder head.  Socket has 3/8” drive for use with a ratchet or breaker bar.