This has a large clasp on one sided, and on the other side:
2.5 inch extender
1 inch extender
this is the perfect layering tool. You clasp your necklaces, one by one, on any part of the extender chain for your desired look. Then you use the clasp to hook the other side of your necklaces. You could even clasp multiple on one chain if you have more than 3 necklaces!
I recommend doing it in the mirror so you can choose exactly where you want to clasp!