craftgrrl | How to add clasps to the end of bracelets/necklaces?

Okay so another question i am using nylon thread and i have no idea how to add a clasp.
Problem is that when i add the first bit of the clasp its fine but when i add the last one and i want it to be flush against the beads there is this massive gap and all the beads move when i want them to stay in place. I hope you understand me its a bit of a weird explanation sorry about that.
:/

Basically the problem is that the end bit of the clasp the last bit to put on does not keep tight with the beads and thus the beads move around and i don't want that.