Yesterday i was given a dozen metal cassettes by someone who told me they were 4x5 cassettes. Obviously they aren't, because they are a lot smaller then the double slides i generally use and they don't fit the back of my Toyo camera. The outer dimensions are 14.5 x 10,0 x 0,4 mm. They are one sided and when opening them they show a nice stretch of dark red velvet, followed by a 9 x 12 inlay. I put an old piece of 9x12 film in it, which fits nicely. The 9x12 inlay can be removed, but you need considerable force for it and i don't see how this can be done in the dark without damaging the film in it. When tehy are removed the cassettes shows a nice spring mechanism to hold in the inlay in place. Does anyone of you know what these are and how to use them?