The Petzl Pirana is a lightweight descending device primarily designed for a single rope. It may also be used with a double rope, but you may not be able to use certain braking positions with them, especially with large-diameter ropes. Petzl recommends 8 to 13 mm ropes for this figure-eight descender. Use of the Pirana is easy as it is not necessary to remove it from your harness for rope installation.
HMS locking carabiners with a cross section of 12 mm, such as Petzl Attache or William, work best with the Petzl Pirana. This is because such ‘biners fit snugly into the small attachment hole in the Pirana, thanks to a plastic attachment that grips them. In fact, the fit is so tight that you have to apply some pressure to get the carabiner in. This prevents them from getting accidentally loaded across the gate.
The Pirana features three braking positions. Your choice from among these depends on your weight, the diameter of your rope, and the terrain. Two supplementary braking spurs provide greater control over speed of descent by allowing the increase or decrease of friction. This allows a smooth descent even if you are carrying heavy packs.