I have a half plate camera. I've found that mine will accept standard size 5x7 film holders. Since 5x7 film can be found, while half plate film is impossible to find (although it can be cut down from 5x7 or 8x10), I suggest you buy 1 5x7 film holder and try that in your camera. If it works, buy 5x7 film. If you still want to do 4x5 film (for example, if you have a 4x5 enlarger), then you can mound 4x5 film in a 5x7 sheet film holder easily, it will slip in the usual film rails. You may have to cobble up something to keep it centered.