A Petzl Stop is a descender used primarily in caving

Caving

Caving—also occasionally known as spelunking in the United States and potholing in the United Kingdom—is the recreational pastime of exploring wild cave systems...

 and industrial rope access made by the French company Petzl

Petzl

Petzl is a world leading manufacturer of climbing gear, caving gear, work-at-height equipment, and headlamps based in Crolles , France. The company was created by the cave explorer Fernand Petzl in the mid-1970s...

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Usage

The Stop is for use with single ropes between 9 and 12 mm in diameter and is usually attached to the harness via a carabiner

Carabiner

A carabiner or karabiner is a metal loop with a sprung or screwed gate that is used to quickly and reversibly connect components in safety-critical systems. The word comes from "Karabinerhaken", meaning "hook for a carbine" in German.-Use:...

. The rope is then threaded through the cam and bobbin by undoing the safety clip and moving the swinging side plate to the side. The swinging side plate facilitates insertion and removal of the rope without the need to disconnect it from the harness, making it less likely to be dropped on long abseils

Abseiling

Abseiling , rappelling in American English, is the controlled descent down a rock face using a rope; climbers use this technique when a cliff or slope is too steep and/or dangerous to descend without protection.- Slang terms :...

. As the Stop is a self-braking descender, it is possible to release the deadman's handle to stop the descent. This functionality allows the user to stop and maintain his position while abseiling.