Ascend or descend using doubled rope technique (DdRT) - all in one unit! Works the same way as a friction hitch but instead of friction cord the Lockjack has an aluminum cam which pinches the line when under load. The cams can be easily replaced - the unit comes with two different size cams - one for 11-12 mm rope and the other for 12-13 mm. Your rope will run freely through the Lockjack when not under load ensuring no slack in your line. Great for limb walking. Includes a built-in swivel to eliminate twisting of your line. This device is very sensitive and only suitable for experienced climbers. CE Certified.