The V Twin is a variable friction belay device. It is made from stainless steel for durability and better heat dissipation. It stays a lot cooler on long abs when compared to it's aluminium counterparts. DMM spent a long time playing around with the directional teeth in the body so that they allow you to easily control the friction without the side effects of the ropes sticking when you want to pay out quickly. This unit works well on all ropes from skinny 8.0s to fat 10.5s - as usual all the DMM office personnel were roped in to test this comprehensively at the local wall, however the prize goes to Mr. Desroy for taking repeated falls onto a (backed-up) new 8.0mm rope.... It uses the same nylon covered retaining wire as that used on the Bug because this has a proven history of good durability