This is a handy little tool. It may seem very simple but it can prevent a lot of re stringing when assembling bracelets etc.
It's called a Bead Stopper. The little spring opens up and clamps around your stringing medium. I've used it on Fireline type medium, waxed cord, ribbon and elastic and it holds well on all of them. It holds pretty tight. I can pick my pieces up, and handle them quite a bit without the worry about the beads sliding off.
I like that I can work on assembling my piece without using crimps. I can take out or add beads without much hassle.
I purchased mine at Micheals. I've seen them in most bead shops. A small purchase that will save you a lot of grief!