The AIR FORCE 1 belay device can be used with single ropes of a diameter between 8,5 and 10,5mm. The V-groove runs smoothly enough to pay our slack easily, but also offers extra friction to improve rope braking while belaying and optimum energy absorption should the climber fall. The wide, smooth groove also avoids parasitic friction on edges and keeps rope wear to a minimum. For added security, each belay device has an individual number that guarantees its traceability.