Came across an odd holder. It's 4x5 and slotted. Has a dark slide and inside a removeable piece with springs. Clearly would not hold a piece of film properly unless somehow supported, but could hold a glass plate. The backside also slides out. It would appear that you load it from the back (first the glass plate or film, then the insert). Pictures at http://home.comcast.net/~hgolds/graflex_4x5_plate_holder.jpg

I think this is a glass plate holder but would appreciate confirmation. Thanks.

Yup, that's what it looks like to me. Not that easy to find these days. Nor are plates. That particular holder will fit only cameras with the Graflex back, not Graphic or Graflok.

That's interesting - it doesn't look anything like my plate holders. Mine look pretty much like film holders except deeper and without the little metal lips on the sides to hold the film. The plates are held by a slot at the closed end and a groove in the flap.

I have Graflex plate holders which are like film holders except they are thicker. Mine came with metal sheaths which can be inserted and have side grooves which will hold film. So they could be used for plates or sheet film. I have used them for exposing sheet film and they work fine.