My fixed Stewart screen uses 1.5" square tubing and I have seen on this forum that they have a fancier version that is different.
On mine I made some brackets to go from the wall to the frame from 3/4" angle iron. There are two threaded mounts in the center of the 1.5" square tube on the top and bottom.
The screen snaps on the rear surface of the square tubing and is about 1/8" away from the rear face of the tubing due to the snaps.
I don't remember the dimensions on the supplied brackets but couldn't use them anyway.
Call Stewart and as them to fax you the screen and mount details and that will help you out also.
I also had them put blackout material behind the screen, and they did it at no extra cost. This will keep any light that goes through the screen from bouncing back and lowering the contrast ratio. I highly recommend this.
Good Luck, Don