I would like to learn as much as I can about a large square I picked up. Overall dimensions are approximately 30" X 12". I can't find a brand name on it. The blade part is stamped "Cast Steel" and "Warranted". There are no graduations. The black part appears to have been painted by hand. Would this be used in a particular industry such as shipbuilding? How common are squares this size? How old might it be? Would this be of interest to a collector?

wish i could tell you who and where, but i haven't a clue...sorry.   it IS a nice tool though. 

The shape and knurling of the nut for the blade clamp is distinctive from one manufacturer to another.  But I don't know where online you could find a chart pointing you in the direction of who made that.  It's a truly neat tool; wouldn't have broken my heart to have found that in an estate sale.

I decided to offer it for sale on Facebook Marketplace.