The ALF is a two-way locking pulley, designed to be used as part of a continuous loop system, in order to protect climbers as the climb vertical structures. The ALF is ideal for use on ladder climbs and in Ropes Course applications.

Fall distance is limited to a few centimetres, so following a fall, most climbers are able to regain their grip on the structure, to resume their climb, unaided by staff. When a rescue is required, this can often be carried out from the safety of the ground.