I am trying to find the gobo size for an Altman 4.5Z ellipsoidal. It is an older, low wattage instrument, and the data sheet doesn't specify a letter size. However it does have this for a pattern holder in the data sheet: Pattern Holder, 2 7/16" diameter opening, 3 3/8" wide. I haven't found a site with a definitive answer if it is a standard size or not. Maybe I'll just have to order large and trim to fit, which would probably be fine.