The Edelrid Bankl plate can be used on single or double rope. Directions for its use are forged into the plate. For belaying, a Munter belay is appropriate, while rappelling is done in a free-running configuration. See the Yates Belay Slave illustrations for details.
I tried a free running rappel on doubled caving rope one time. Our stiff ropes are not designed for such sharp bends, and it sounded like the rope was being torn apart. Perhaps it wasn't, but I still don't like to use this device on stiff ropes.
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©2007, Gary D. Storrick