Here's what other sites are saying:
Petzl Big Wall & Protection Tandem Speed Pulley P21SPE.
The Petzl Tandem Speed Pulley is a Climbing pulley for lower-angle tyrolean traverses. The Tandem Speed Pulley Uses stainless steel sheaves for durability. The fastest transport pulley by Petzl, at a maximum allowed speed of 20 m/s. ZOOM! The sheaves Are mounted on sealed ball bearings for sustained speed. The pulley is capable of transport via rope or cable and can attach up to three carabiners. Enjoy sending yourself (or a buddy) across to the other side. Features of the Petzl Tandem Speed Pulley Stainless steel sheaves for excellent durability Sheave mounted on sealed ball bearings for excellent efficiency Accepts up to three carabiners to facilitate use
The Petzl Tandem Speed Double Pulley is made with stainless steel sheaves and ball bearings for excellent durability and sustained speed.
The Tandem Speed Pulley from Petzl is the fastest of the transport pulleys and is specifically designed for ropes course zip lines. It's an efficient double pulley for use on ropes and cables.
- Mountain Gear