Hello 4x5 printers,
Here's a much later addition to the topic!
Although the previous explanation for the names Durst gave the enlargers sorta makes sense, the 1000 was also a 4x5" (as well as the 900 with the CLS450 head, I believe), so I don't know what to make of that. I thought it had to do with the available heigth of the column (about 1000 and 1200mm for the enlargers of the same names)...
Nevertheless, to my knowledge there was only one Femoneg for the whole world (mine have either black or brown knobs) and I bet the narrow minded engineers never imagined that anyone would want to print with a black binding, or maybe they thought the Femogla's (glass plates) were good enough for the few weirdos who did. So yes, the standard bottom Femomask's do crop in the image and the top ones are big enough not to, but their straight edges cause problematic reflections.
Back in the day, I started by beveling those with a file and painting the metal flat black. Now I have a complete set of bottom Femomask's (for the useful springy prongs) made bigger and beveled by a machinist.
I think the Femoneg AM came out in the nineties, to make full use of the Pictochrom 5x5 lightbox. Its corners are more open, allowing for the full size of the 4x5 film. Note if the Femomask's do fit in the AM (as shown in the image), only the glasses that come with it cover the whole surface.
Similar topic, the 1200 came with 24x36, 6x6, 6x9 and 4x5" Femobox's. The Pictochrom's are 24x36, 6x7, 4x5" and 5x5". But somehow, the so called 6x7 doesn't cover the whole image, it is lacking a few millimeters in length, which causes about 1cm of a 12x16 print to be significantly lighter. So I only use it for 4,5x6 and 6x6. For 6x7, I have a special Pictobox with the inside of a Femobox 6x9 to which the late Durst USA guy added a top diffusor, necessary with the Pictochrom...