Help identifying lens board

[Mattk]

I have this lens and another (150mm Xenar 4.5) that came with some other gear and I’m trying to figure out whether the are from an enlarge, process camera, camera? Any help would be appreciated.211668

[NER]

This lens does not appear to be mounted in a shutter, and the board is not unlike one that might be fitted to an enlarger, e.g., a D2, so it may have been used for enlarging but that is hardly dispositive.
Here - https://api.offerup.com/item/detail/944259158/ -is an image of the same lens mounted in a shutter; however, that does not mean someone could not have used the lens for projection enlarging.
I have no idea why the corner of the board would be cut like that.

N. Riley
http://normanrileyphotography.com

[Dan Fromm]

Dimensions?

[Mattk]

4 7/16” square