Hey all, was about to start rebuilding my carb and realised that this doesn't look right..

Has anyone got an idea what's supposed to go in here, because it doesn't look to be a threaded hole

If I can replace a part or put a bolt in I'll be happy.. If not doesn't anyone know of a replacement, either re-manufactured or straight bolt on, which isn't a Polski carb?
Thanks all,
Matti.
