The Unicender utilizes unique friction plates that allow it to advance easily with minimal friction, and virtually no Sit Back, giving you the most efficiency per stride. Descending is just as easy: by looping the rope around the plates in SRT as shown below. Additionally, the Unicender attaches conveniently mid-line. For rope sizes 11 to 13mm, or 7/16 to 1/2. For both SRT and DdRT climbing technique.Virtually no "Sit Back" while ascending. 10.9 oz (308 gm). The item "Unicender Arborist Tree Care DdRT Tool SRT Device Rock Exotica" is in sale since Saturday, July 23, 2016. This item is in the category "Sporting Goods\Outdoor Sports\Climbing & Caving\Carabiners & Hardware". The seller is "monarchrope" and is located in Houston, Texas. This item can be shipped worldwide.