Stanley Proto JFP9BSET Proto 9-Piece Spark Plug Set - Black Includes three different sizes and three different configurations most commonly used when working with spark plugs 9/16-inch, 5/8-inch and 13/16-inch spark plug sockets in standard, universal and extra deep lengths Universal styles for most applications 3/8-inch square drive sockets feature a rubber insert to securely grab the spark plug Each socket features a knurl for easy hand turning