Crochet hook (I used H)
Rnd 1: Chain 7 slip stitch together
Rnd 2: Single crochet into the circle until you get around slip stitch to first sc.
Rnd 3: Sc 2, ch 1 turn sc 2, ch 1 turn sc 2, work down side of it *sc 1, ch 1, sc 1 chain 1 turn sc 2(1 in sc one in ch), ch 1 turn sc 2 work down side* repeat till you are around.
Sorry about Rnd 3 being so confusing I made this before I went to sleep so I was tired and I do not remember how I did it. I used this cog as a reference to make it Here
Made relatively the same the same at the start put you chain 3 and work down the chain slip stitch to middle and work around
Chain until you can fit it around your head nicely and then slip stitch it together then you can stitch it more together further and maybe knot the 2 yarn pieces together and cut them.
You could just make a circle to put the gear on by chaining around 10 and having it on there and stitch it together. Or you could just have it on the Necklace without the round piece on it.