Steve, Thanks for your input. But my problem is with the construction of these brand new holders and the fact that the distance between the septum and the film rails is well over .021. That allows for three sheets of film to be loaded into one side of the holder with ease. These holders were built to my camera as I sent my camera back to the manufacturer to fit the holders to the back. The fit of the rib lock is not the problem. When loading a sheet of 8x20 in the vertical position the film sags at the bottom to where it is touching the film rail so this is pushing the top of the film back against the septum. Due to the slop in the film slot this is allowing light to enter around the film rail.Thanks, Robert