The threads on the Supramatic shutter will fit through the hole for the Copal #0. If you use a board with a #0 hole, you will have to mount the retaining ring with the flat side to the board (i.e., with the shoulder away from the board, that is, if you have the original retaining ring).
Originally Posted by Lobalobo
Just FYI, the Supramatics were designed for a 1.5-inch hole (~38mm) and the shoulder on the retaining ring took up the slack and protected the threads on the shutter. If you have the original retaining ring and wish to mount it this way, it is often not too hard to sand or file a #0 hole just a bit larger till the retaining ring shoulder will fit. That is a better mount IMHO.
I love my Ektar 203 and use it a lot.