Need help identifying this AAC muzzle device

[Xennocide]

Hey guys, new here but figured one of you could identify this so I know what I can use it on.
Its an AAC 51t 3 prong deep socket muzzle device but I've never come across one with a flush base. I picked it up at a local sale and want to know what threading and barrel diameter it will fit on?

 

[FuhQ]

I would assume something .750" or less...Which is standard AR barrel taper from the gas block to the muzzle (so the gas block can slide over it and down to the gas port shelf. I don't know what the largest barrel it can handle, I'd assume naturally anything that is smaller in diameter than the bottom of the teeth? What it can be used with is any AAC can that used a 51T mount. Not sure if it is interchangeable with the 19T mounts.

 

[smokin.338]

take a pic of the threaded area at base to tell...

 

[Texasflyer]

If you can drop a 30 cal bullet thru it then its a 7.62, if not its 5.56. I got my aac flash hider for 10 bucks in a bargain bin for my ar 10. Its flush on the rear also. I installed mine without a crush washer cause it clocked right.

 

[Xennocide]

added some more pics. I believe its for 30 cal (thanks for the idea of dropping a 30 cal bullet through it) but seems like it would have to be a pretty thin barrel. I can't even find any examples of this model online. Is it an early production maybe?