They're made by Dave Kiff at PTG. You can order a bolt of whatever diameter you'd like directly from him, or get them from Midway in the stock size he makes, which is bigger than a regular Rem bolt. I think they're about .695" IIRC. They are very nice, and quite useful if you have a rifle with a too small bolt, or you want to change to a different bolt face without cutting on your original one. They're also nice if you want a Sako style extractor, since he relocates the ejector on the ones furnished with the Sako cut so the cases go out the ejection port instead of up into the scope. Keep in mind they don't come with a handle, so you'll need one to make it work. I've installed quite a few of them and have been very happy with his workmanship.
