Ascenders are used when climbing featureless rock mountains where it is difficult to find edges, cracks, or pockets to hold on to, or when climbing very tall trees with few strong branches along the way.
The CMI Hardware Ultracender is a good specimen of ascenders. These are usually purchased in pairs, one configured for the left and another for the right hand, although you can buy only one unit for either hand.
The body of Ultracender is made of solid aircraft aluminum that has been machined and extruded. The springs and other operating parts are all in stainless steel.
The cam that presses against the rope is a 4140 chrome-moly steel. This alloy of chromium and molybdenum results in an excellent ratio of strength to weight. It is also far stronger than standard steel. Indeed, it is stronger than most knife blades and files. It is finished with a non-metallic coating that resists corrosion. The conical rope penetrating teeth on the cams minimize abrasion of the rope’s fiber.
A thumb notch is incorporated at the top of the cam to simplify its full retraction. This makes it easier to attach the ascender to climbing ropes from 6 to 16 mm. A molded handgrip provides a comfortable hold, something appreciated especially on long hauls.
The CMI Hardware Ultracender measures 19 x 8 cm, weighs 270 g, and has an MBS of 4,600 lbs.