Hip key! One of the most important skills in aerial silks (and other apparatuses)! But why? What makes it SO INCREDIBLY VALUABLE?
Also known as a hip lock, this wrap puts you in a position of relative restfulness. I say "relative" because no matter what you're doing, when you're training aerial you're working hard.
But it supports you around your hips, allowing the hands to come completely off if needed. You can describe the wrap as a form-fitting shelf under your bottom hip.
The shape of the hip key: The fabric descends from the ceiling, passes the junction of upper body and lower body to continue under your bottom hip/upper-outer thigh, and is then redirected UPWARD between legs with the tail draping over the low back. In short: down, up, down.
The wrap doesn't fall off because by winding into the pole with your body you have "closed the loop. " Winding into the pole involves stacking your hips, which causes the tail to go UP, in toward the pole, and then down. If your hips unstack (unwind), your loop opens away from the pole and it unwraps. If you go vertical, your loop opens and falls off. It is only the stacking of the hips that allows the wrap to be secure.
Now let's look at that shape (high qual courtesy of MS paint).
If the tail does not land on the back it will slightly "open the loop" and can fall off, but this is less likely to happen if the legs are trapping the tail with a good squeeze.
The wrap works because your center of gravity is close to your hips. If it were at your feet or chest, you would tip out with gravity.
From a hip key you can rest and spin, transition directly to your hands and be wrap free, or transition to a thigh hitch or an unsupported knee hook. You can roll up all the way to an s-wrap, split your poles to get to swing seat, and build a variety of wraps. With the fabric securely wound around the hips, there are many possibilities for how to use the tail(s) and work with the pole(s).
A few common mistakes:
A hip key executed without applying technical cues.
A hip key executed with good technique.