I recently picked this up with the assistance of one of my good friends. It’s an original M16/M16A1 armorer wrench and not a reproduction. The rear is marked “Wrench For Rifle, M16/M16A1” and then has the old part number on it.
This wrench allows for installation of the original 3 prong flash hider, the improved flash hider, and barrel nut.
Great find! It’s been a LONG time since I’ve seen one of those.
I’ve never seen one so thanks for sharing.
That heavy huh? 
I kid.
I’m intrigued, where did you find it? What are you gonna do with it? To be honest, I don’t know much about them and I’m a sucker for history.
I have one of those tools too.
I have 2 of those. They are pretty cool.
I have one of the later production ones that doesn’t have the part for the three prong. Oddly enough it has the same part number on it.