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There are different types of locking carabiners. A screw-gate carabiner requires multiple rotations of the screw in order to lock it. A twist-lock carabiner locks automatically whenever you close it.

Are twist-lock carabiners dangerous for some applications?

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A rope running across the rotating sleeve of a twist-lock gate can open the karabiner.

Animated GIF showing rope opening twist-lock gate.

Background
There are different types of locking gates on karabiners:

  1. Screw gates: These have a threaded sleeve which is screwed manually to lock the gate.
  2. Twist-lock gates: These lock automatically when closed, and need a quarter-twist to unlock
  3. Triple-lock gates: These have an an extra action to perform before twisting, often sliding the gate upwards.

This list is not exhaustive and other types of gates exist.

Twist Locks
These karabiners can provide a sense of security but the user might not be aware of the risk of the rope opening the gate. In certain circumstances, they provide enough security for their intended use but this should always be a conscious decision after the risk is evaluated by a competent person. In most cases, either a screw gate or a triple-action gate will be more suitable.

Comparison to Screw Gates
So why does the same not happen with screw-gate karabiners? Theoretically, it could but a screw-gate needs multiple rotations before it unlocks. The rotating sleeve also tends to be shorter, making it harder for the rope to run over it.

Here are the statistics of three karabiners I had to hand:

  • Twist lock: 0.25 full rotations to open, 4.5 cm rotating sleeve
  • Screw gate 1: 2.25 full rotations to open, 2.2 cm rotating sleeve
  • Screw gate 2: 2.5 full rotations to open, 2.3 cm rotating sleeve

Single-action gates
Twist-lock karabiners generally fall under the broader category of single-action karabiners. Other karabiners in this category can also suffer from the rope opening the gate. For example, there is a push-lock gate which requires the user to simple push/pull the sleeve to release the gate. If the rope catches on the sleeve, it can open the gate in a way similar to the twist-lock.

For completeness, the triple-lock gate mentioned above would come under the broader multi-action gate category.

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  • Double gates don't have any problems like this, right?
    – endolith
    Apr 17 at 1:24
  • 2
    @endolith, Double gates are much more secure, as you can probably tell from the difficulty of using them quickly. I'm told you get used to them (and have seen it), but personally I've never managed. I can't answer with 100% certainty but I would be very surprised if a rope could accidentally open them; it would have to get under the outward opening gate.
    – Mehmet
    Apr 17 at 6:53
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There's nothing inherently dangerous about different types of carabiners, but each type has a specific application.

A twist-lock carabiner is not normally used on a climber's rack. Climbers normally carry mostly non-locking carabiners plus a smaller number of screw-gate lockers.

The main application I've seen for twist-lock carabiners is in climbing gyms, where they're the biners that are permanently attached to a GriGri in a toprope setup. In this application, the biner is being clicked through the belay loops of the belayer's harness, rather than having a moving climbing rope clipped through it. This means that the rope can't open the gate by being dragged over it.

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