I originally wrote and photographed this tutorial for the Artisan Beaders Blog, but I decided to share it here too.
Let's make a simple clasp. Start by cutting 2 pieces of 18 ga wire: one piece is 2" and the other is 1 1/2". Make sure the ends are cut flush. Trim if necessary. I like 18 ga for this style clasp, mostly because of the style of necklace that I use it with. It can certainly be done with 16 ga wire for a heftier piece of jewelry.
Using the larger length of wire and round nose pliers, make a small loop at one end and a slightly larger loop at the other, both on the same side of the wire.
Choose a dowel. I use a size 10 metal knitting needle, but you could use a Sharpie pen or a wooden dowel. A size 13 knitting needle works well too, resulting in a much curvier clasp. Place the wire on the dowel, off -center, being sure to keep the end with the smaller loop as the shorter end.
Hammer the curve with a chasing hammer on an anvil or bench block. This is not a necessary step, but I like the way it dresses up the clasp. At this point, you can also use a plastic mallet to hammer the clasp to work harden it.
Using the shorter piece of wire, make a small loop at one end with round nose pliers.
Remove the wire from the pliers and place it so the loop is above the jaws, at the very widest point, up against the joint. Be sure the loop facing away from you.
With your fingers, bend the tail end of the wire around this wide spot, forming a figure-eight.
Again, remove the wire from the jaws of the pliers and re-place it on the other jaw. This allows you to continue bending the wire to form a true figure-eight. Trim the excess wire with flush cutters. You can hammer the curved points as you did with the other part of the clasp.
I usually make a whole bunch of these in one session and put them in the tumbler for 2 - 3 hours.
That's it -- now go bend some wire!