I apologize for not describing this device correctly but I don't really know what to call it.

I got the "contraption" in a box of misc darkroom items at an auction. It appears to be useful as a universal negative mask. There are adjustments on two sides that move shutters across the 5 inch square opening -- essentially permitting one to create an opening anywhere, of any size within the square. (see pictures)
I plan on adapting this to my 4x5 chromega enlarger.
The only markings on it are "Charels Beseler Company Cat. No. P 106"
I've not been able to find information through the typical search environment. The Cat. number doesn't seem to follow current Beseler numbering systems.

My questions to anyone who has seen, or might even have, one of these are:
  • Is it complete?
  • Which Beseler enlarger is it designed for?
  • Or for that matter: What is it called?

Thanks for any insight you can provide....