| Main use | Rappel backup |
| Advantage | Releases & slides one-handed |
| Wraps | Typically 4-6 |
| Difficulty | Intermediate |
The autoblock, or French prusik, is a friction hitch wrapped around the rope and clipped back to itself, used mainly as a rappel backup. Unlike a prusik it releases easily under load and slides one-handed, so a rappeller can tend it as they descend and have it grab the rope if they let go of the brake.
How it backs up a rappel
Tied on the brake strand below the device and clipped to a leg loop, it slides while you hold it loose and grabs the moment you let go — see rappelling.
Autoblock vs prusik
The prusik grips harder but is hard to release; the autoblock slides and releases easily. See autoblock vs prusik.
Use it right
Use 4-6 wraps and always test it under body weight first.
Frequently asked questions
What is an autoblock used for?
It backs up a rappel: tied on the brake strand below the rappel device and clipped to your leg loop, it grabs the rope and stops your descent if you lose control of the brake. As you rappel, you loosely hold it open so it slides, and it grips the instant you let go.
What's the difference between an autoblock and a prusik?
Both grip the rope, but the autoblock is designed to release and slide easily even under load, which suits tending it while rappelling. A prusik grips harder and can be tough to release once weighted, making it better for ascending but more awkward as a moving rappel backup.
How many wraps does an autoblock need?
Usually about four to six wraps, adjusted to the rope and cord so it grips reliably without being so tight it won't slide. Always test that it grabs under body weight before committing to the rappel.
Sources
- Rappel backups — American Alpine Club