Fairmount 9/16 x 5/8 Open End Wrench (535-OW)

Fairmount 9/16 x 5/8 Open End Wrench. How old is this? Well, my great grandfather bought this deal from the US government I don't know how long ago, and they have been sitting in a box in the basement ever since. Surprisingly little rust on them. Beefiest open end wrench I've ever seen. 8 1/2" Long. - Fairmount 9/16 x 5/8 Open End Wrench