Hole on socket locks on to drive tang, keeps socket from slipping off or sticking to fastener. Pro grade tools meets or exceeds ansi spec b107.2. I got what i oredred and recieved it in 3 days! 01/21/09 absolument parfait very good merci! 01/02/09 the osldering station is awesome!Fair pricing, product as shown. Impact socket set 38 sae metric 4 pack combo 36 air tool accessories.