The Lockjack was the first piece of hardware on the market that could totally replace the friction hitches used on climbing lines. Like a Mechanical Prusik, the Lockjack works as both an ascender and as a descender in the doubled rope technique (DdRT). The advantage of the Lockjack is that friction is applied to the rope with a smooth aluminum surface which causes less friction while climbing for an effortless advance, and a smoother more easily controlled descent.