Back up device ascender that works well for a rappel backup on both single and double ropes. This is a great replacement for the old prusik friction knot. A mechanical replacement for self jamming knots Prusik, Machard, etc.. a When positioned below the descender, the SHUNT can be used as a back up device to protect a descent on rappel. a Brakes when device is released. Certification: CE, UIAA Technical specifications: For use on single ropes 10 to 11 mm or double ropes 8 to 11 mm 188 g Note that this item of climbing safety equipment is non returnable. Please call us toll free at 877 236 8428 or e mail bentgatebentgate.com with any questions.