Just the other day, I had need of a big adjustable and I remembered one I got from my dad. As I was using it, I was wondering about the Diamond brand, as I hadn't really ever noticed it before. That's why I love this forum. Looked here tonight and here's a thread about this very thing!
I looked around and found I had two of them, a 15" & a 10 ", but from different eras I think:
See, the logo's are different:
And the 10" is marked in MM's, too:
But then, I noticed something else. I was born in LA, and when I was a little kid, every time we happened to pass by this certain building, dad would always tell us about it being the biggest job he ever worked on (he was a plumber). As I was looking the 15" over, I saw that someone had engraved 'Arabian Gardens P, H & E' on it:
That was the name of the building! What a blast from the past! I was born in '58 and I'm pretty sure dad worked there before I was born, so if he stole that wrench from the Plumbing, Heating & Electrical dept of the finished project, it must be at least older than late '50's.