For fast, safe connection to screws/bolts with internal hexagon. Twisting the button on the back of the handle spreads the hexagonal tip so that the adapter fits firmly into internal hexagons with 5 mm wrench size. This results in multiple contact points that enable low contact resistance. The adapter can also be operated by hand when under load. The fixed ? 4 mm socket in insulator is suitable for fitting spring-loaded ? 4 mm plugs with rigid insulating sleeve. Design: 6 mm with gray button.