ISC D4 Descender
The D4 Descender features a unique and innovative progressive cam action, which offers precise control at slow or fast speed. The device 'fails to safe' (the device locks if the handle is released) and also has a panic brake feature (if the handle is pulled down in panic when in freefall then it locks the device - The progressive cam design means that this panic brake is not overly sensitive in normal use). The device is made from a high grade aluminium and has a stainless steel cam, axles and top bobbin which should ensure a good degree of longevity. The beauty is that the internal workings are cleanable.
The D4's other selling points are that it is rated to 240kg and does not require extra friction to operate at the top end of its range. Operationally the D4 has a smooth rope run through the device and when the user is not in full suspension, such as if working on an incline (like an embankment), the design allows the cam to be squeezed open using your thumb to allow rope to feed through gently (no need to operate the handle). Finally, the D4 works well in a belay mode as well as when put into a system such as a Z rig.
Suitable for low stretch ropes (EN1891) 10.5-11mm