Again, depends on the size of the trunk. For a trunk about as wide as your pnky, you're going to need some pretty thick wire, I'd say 5mm or better. Most bonsai shops I've seen only go up to 6mm in regular stock. If you're wanting to bend something bigger than that, as your first tree, I'd say you're getting WAY ahead of yourself. Have you purchased any books on styling, growing, anything yet?