The 1200 uses a Femoneg negative carrier, a 2-part metal frame hinged at the backthe AM version for the American market which, I believe, has white or light grey knobs, and the regular version for everywhere else, which as black knobs. I mention this difference because the masks or inserts and glass are not the same size. Both versions use inserts or glass with clipped corners.
Durst makes masks or inserts that fit the femoneg, specific for a certain size negative. These inserts come in pairs, top and bottom. Or, you can remove both inserts and insert 2 pieces of glass (usually the top one in anit-newton) and have a glass carrier.