Here's what other sites are saying:
The Tandem Pulley from Petzl is designed for smooth and efficient Tyrolean traverses on rope.
On Sale. Free Shipping. Petzl Tandem Pulley FEATURES of the Petzl Tandem Pulley Aluminum sheaves mounted on self-lubricating bushings for efficiency Accepts up to three carabiners to facilitate use
Fixed sides and self-lubricating bearings, ideal for use with rope clamp/grabs and OK or AmD carabiners from the PETZL range.
The Tandem Double Pulley from Petzl is designed for smooth and efficient Tyrolean traverses on rope.. . . Sheaves mounted on self-lubricating bushings for good efficiency. Maximum allowable speed: 10 m/s. Attachment point accepts up to three carabiners to facilitate use. For use with ropes of maximum diameter 13 mm.