The Figure 9 carabiner lets you quickly fasten — and quickly loosen or adjust — a small-diameter rope to a fixed point without a knot deploying a clever combination of friction and angles. To those of us with knot-dyslexia, this is a real boon. The only requirement: your fixed attachment point must feature either a place to clip the carabiner (i.e. a metal loop in a pick-up truck bed or a thin, sturdy tree branch), or something around which your line can be looped. That could mean securing a Tarptent to a tree, improvising a handle around a bundle of cables, or securing a travel clothesline between window-grate and curtain-rod.
All you need to do is pull the rope through in the right sequence and finish with the rope’s loose end tugged into the notched “V” section to keep the rope attached and taut. There are actually multiple sequences and ways to work the geometry. Three methods are diagrammed in the instructions that come with the carabiner (see below).
Thus far, I have used the devices only with standard-issue parachute cord, but they’re sized to work with a range of small-diameter ropes. Though the tying system looks suspiciously wimpy, I’ve found it is as robust as promised. I ordered the Figure 9s to replace the mesh netting that came with the roof-rack basket on my car. Not only do these make a decent replacement (i.e. riding around with a kayak strapped to my car this summer), but tying one more knot under the car is something I’m glad to skip. Note: the device is anodized aluminum and weighs a bit more than I expected (slight downside to ultra-light hikers); still, “Not for climbing” is printed on the packaging, repeated in the instructions, and emblazoned on each carabiner. I think they mean it.