Key takeaways
- The autoblock is a friction hitch used as a backup for rappelling.
- A cord loop wraps the rope below the device; it grips and locks if you lose control.
- It's easy to release under load, making it ideal as a rappel backup.
- It provides a hands-free safety, significantly improving rappel safety.
This is general educational information, not instruction. Rappel backups are life-critical — learn and verify them hands-on with qualified instruction.
What the autoblock is
The autoblock (or French Prusik / Machard) is a friction hitch most commonly used as a backup for rappelling. A loop of cord is wrapped around the rope below the belay/rappel device and clipped to the harness leg loop. As you rappel you hold it loose so the rope feeds through; if you let go, the autoblock grips and stops your descent.
Why it makes rappelling safer
It’s a hands-free backup brake. Normally a rappeller’s brake hand is the only thing stopping them — if they lose control (rockfall, a falling object, losing consciousness, or simply letting go), they could fall. The autoblock automatically grips and arrests the descent if the brake hand comes off, a crucial backup that has prevented many rappelling accidents.
Before a long rappel, a climber rigs an autoblock on the rope below their device and clips it to their leg loop. Partway down, a falling rock strikes their hand and they lose their grip — but the autoblock instantly grips the rope and holds them, where without it they would have fallen.
Why it’s ideal for this role
The autoblock grips when needed but is relatively easy to release under load — you grab and slide it to keep descending. That releasability is why it’s preferred for rappel backups over hitches like the prusik that can lock down hard. It’s one of the friction hitches (alongside the klemheist) in the essential climbing knots.
The bottom line
The autoblock is the go-to rappel backup: a friction hitch wrapped below your device that grips and stops you if you lose control of the rope — a hands-free safety that has prevented countless rappelling accidents. It's preferred for this role because it releases easily under load so you can keep descending. Every rappeller should know it as a core safety skill.
Frequently asked questions
What is an autoblock?
The autoblock (also called a French Prusik or Machard) is a friction hitch most commonly used as a backup when rappelling. You wrap a loop of cord around the rope (or ropes) below your rappel device and clip it to your harness leg loop. As you rappel, you hold the autoblock loose so the rope feeds through; if you let go, the autoblock grips the rope and stops you.
How does an autoblock make rappelling safer?
It acts as a hands-free backup brake. Normally a rappeller's brake hand is the only thing stopping them; if they lose control (from rockfall, a falling object, losing consciousness, or simply letting go), they could fall. The autoblock automatically grips and arrests the descent if the brake hand comes off, providing a crucial safety backup that has prevented many rappelling accidents.
Why is the autoblock good for a rappel backup specifically?
Because it grips when needed but is relatively easy to release under load — you can grab it and slide it to free the rope and continue. This releasability is important for a rappel backup (you need to be able to keep descending), and it's why the autoblock is preferred for this role over hitches like the prusik that can lock down hard and be difficult to release.
Sources
- Rappel safety & backups — American Alpine Club
- Knots & rappelling — The Mountaineers