The Toyo 69/45 Roll FIlm Holder is designed to mount to any Graflok-style 4x5 camera back, letting you shoot 6x9cm images on standard 120 rollfilm. Toyo put rails on the sides so you can also try to stuff it under your groundglass, but we do not recommend it: this thing is 4cm thick, which is big enough to damage many spring backs. So, you can, but maybe don't. Some cosmetic wear, with a very small piece of the rail cut away: this is on a side which will not affect function, so it won't cause you any issues, but it's still worth noting. Good light seals, good function and frame spacing.