One of my most used tools are these wire wrapping mandrels. I don't have to worry about making inconsistent sized loops when I use these. They come in two sizes, one for smaller diameter loops and a larger size for bigger loops and clasps. I picked up mine for a very reasonable price from the Contenti Company but Widget Supply also has them for about the same price.
(posted by Cindy Gimbrone, WireHead and blogging glass beadmaker.)