It's US in a Supermatic with #0 size. The Maximar hole for the Compur is somewhat larger at 39mm. So you need to be careful with centering. The Supermatic has a wide flange that covers the hole. I suppose I should take it into the darkroom to double check for light leaks. Funny thing was the Ektar came to me mounted on a real Linhof board. Taking it off I found out that the postioning screw was still installed but the board had no hole for it. So it's been mounted slightly tilted for all this time. Guess the previous owner didn't have any problems.