The vast majority of Power sport vehicles require a 5/8" (16mm) spark plug socket, including Harley-Davidsons, BMWs, four-stroke dirt bikes, ATVs, sport bikes, plus many cruisers and touring bikes. Some require a thin-wall and specific length to fit into the head. We’ve addressed the problem with plug sockets in two lengths - 4" and 5" - to handle most applications. Each has a thin-wall hex and an internal rubber grommet to hold the plug in place. Works in conjunction with the Combo Axle Wrench or a 14mm/9/16" end wrench.