This unique and patented design works on 2004–newer Ford F-150 pickup trucks with 5.4L 3-valve Triton V-8 engines. The socket end is 9/16 inch and the soft rubber insert holds and protects spark plug during removal and installation. The extension is part of the socket and easily fits down spark plug tube into the cylinder head. The socket has 3/8 inch drive for use with a ratchet or breaker bar.