Special descender / belay device that easily controls 500 lbs loads. Side plate closes with low-profile, spring loaded safety catch. Simple functional design. Can be placed onto the rope without removing rigging carabiner. Rotate handle counter-clockwise to lock in place. Rotate right to descend or lower load. Rotating handle too far clockwise will engage panic stop function. C ontinued clockwise rotation re-sets the unit. The D4 is a true panic stop device rather than a panic brake device. The difference is that once the panic stop is activated, no other force must be applied to the device. A panic brake style device requires a force input to continue the braking function. Can be used for progress capture in hauling systems and allows rapid conversion between raising and lower. For 3/8" - 7/16” (10.5 - 11.5mm) ropes. See the D5 for use with 1/2" ropes.