circular waveguide standards?

usually EM designers says that there is no one standard diameter, They says that only the design specifications (cut-off, group delay etc) sets the dimension.
I agree, but for my knowledge, some standards exist even if they are very free. The dimensions has been proposed many years ago form Millitech, Hughes and TRG.
At present Millitech still exist.
Hughes and TRG has been sold , at present days, look for Quinstar or Wisewave
http://www.wisewave-inc.com/
http://www.quinstar.com/
http://www.millitech.com/