Three different braking positions to select from before beginning descent and the two supplementary braking spurs allow friction to be varied during descent. Best suited to a carabiner with a cross section of about 12mm (Petzl William).
This provides a tight fit in the small hole, creating a 'rigid' carabiner/descender unit. When paired with a Petzl William the Pirana folds away nicely into the basket of the carabiner taking up less room on your harness and making less noise.
Used correctly, the Petzl Pirana prevents the formation of a lark's head hitch around the body of the descender and reduces kinks in the rope, without decreasing braking friction. Designed for use on single ropes but can be used on double rope (certain locking positions may not be available depending on the ropes diameter).