The Rack Descender by Petzl is a variable friction descender for single or double rope which allows the friction to be varied when the descender is under load to adapt to changing conditions (rope weight, terrain, etc). Final SALE: For safety reasons, we cannot accept returns on load-bearing Climbing equipment. Sorry for being so mean. Features of the Petzl Rack Descender Allows the friction to be adjusted during the descent according to the weight of the rope: The lower bar is removable and easy to put in place Distributes friction and heat to help preserve the rope Does not twist the rope