I'd guess you could use a Graflex septum as as film adapter in a 5x4 plate holder.

In the US Eastman Kodak made quarter plate film adapters to fit 9x12 plate holders, I acquired two brand new with their original box from the US this week week along with a full box of a dozen )and 4 extra) quarter plate film adapters for "quarter plate" plate holders.

Commercial dapters (Kodak, Zeiss etc) usually have strengthening ribs and it's the more simple 3rd party ones that are most similar to Graflex septums.

Quote Originally Posted by Huub View Post
I had a look at the sticky treath on the plate camera forum and have to conlude that they are cassettes for a linhof type camera. Now to find such a camera...
Thanks for helping me out!
You replied as I was writing. You'd need a pre-WWII 9x12 Linhof, however some other cameras took the same holders I'm not sure which, possibly Silar.