To add a bit more confusion: if you buy a new stem you need to make sure that the opening of the stem matches the diameter of the handlebars. Generally speaking, quill stems come in 25.4mm (most flat bars), 26.0 (most road bars), and occasionall 26.4 (some Italian road bars). It's possible to shim them with a strip cut from a soda can, but it's not optimal.
edit: Sorry: just read Michael's post and he covered that.