A Graphic 4x5" film holder is too large. Plaubel listed the following in their catalog:

#97324 31/4x31/4 back for Single Slides 4x5" MX1/537
#97486 4x5" Univesal Holder for plates & sheetfilm SG1/377 (use with MX1/537)

Actual measured dimensions would be approximately 101mmx140mmx7mm for the single shot holder. Or maybe this back takes 9x12 sheetfilm?

Here are some photos. Can anybody tell me where I can find some holders for this back, so that I can use it? Thanks!