The English progression for ULF Cameras that I know is:

12x10", 15x12", 18x16" and 22x20", 25x21".

How does a 16x14" fit into this series.

This is a book type double sided mahogany plate holder of some age. Bought along with a standard 12x10" similarly period holder.
Actually it would prefer a glass plate a few mms longer in both directions to fit better in the recess. The measurements don't match any Continental metric equivalent.

Help, please! I don't want to build another camera.