Wow, Ron. Your usual compendium. I've made a PDF of that link and will file it away against the day I have to dig out the complete set of new brake lines I have in my spares. It will be invaluable.

However, we were talking about the hex on the external part of the bleeder, the one used to loosen/tighten it, not the threaded part that screws into the caliper. I quick look through your material doesn't seem to offer an answer to that question. However, the fact that the threads are SAE and not metric should hint that the hex part is also SAE. So I guess there really must be some sort of 9/32" tool floating around somewhere.