Quote Originally Posted by big_ben_blue
OK, now you got me seriously confused. The inside dimensions of my holder are 13.1 x 18.1; so it's definitely not a half plate. ...
That certainly looks like the dimensions for a 13x18cm plate camera, yes.

I've also got a camera with only one holder. But in my case that's a good thing, as I discover every time I lift the camera and holder: It's a Russian 30x40cm plate camera...