Duo finger trainer. The Duo is a feather-light climbing accessory that has been specially developed for training. It isolates muscles and tendons. With a finger hole and a two-finger pocket (25mm low), Duo prepares your fingers for all kinds of holds! It can be used with an elastic band, a weight or simply body weight. With its smooth design made from recycled rubber wood, Duo offers a soft-touch surface whose comfort and grip will convince velcro climbers.