Here's what other sites are saying:
Features of the Mammut Crag Light Belay Device Very lightweight belay device based on the tube principle Suitable for double, half and single ropes from 7.5 to 10.5 mm in diameter The V-shaped grooves permit controlledretention of drops even at low manual force as well as controlled lowering of the climber
Show up to the first day of belay class with the Mammut Crag Light Belay Device. The Tube principle and V-shaped grooves give you great control while you learn the difference between a dynamic catch and a static one. We're sure your climbing partner will appreciate that lesson.
Mammut Belay Devices Crag Light Belay Device-Grey 22100110101391. 5 to 10.5 mm in diameter. The V-shaped grooves permit controlled retention of drops even at low manual force as well as controlled lowering of the climber.