308 AR upper barrel nut thread sizes?

ERE99

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Having decided to build a "long" AR, I've compiled a few parts over the last year or so from various trades and WTS ads. The other night I decided to assemble the upper.

The upper is an Aero and came with the barrel nut. I have a free float tube I bought by accident (bought wrong part number for one of my AR15s) I wanted to use, but the barrel nut is too small.

I read where there are 2 common threads, 1-7/16 -18 I think and another 1-7/16 with a different pitch. However, this barrel nut is about 1.300" , between the 1-7/16(1.438") thread and the AR-15 standard 1-1/4(1.250")

What does my hg fit?
 
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Have no idea. I've had it a year or so and forgot where I bought it lol. It's just a run of the mill tubular free float handguard with barrel nut. No markings either. Just posting here to see if anyone knows the thread sizes found on the long ARs
 
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Have no idea. I've had it a year or so and forgot where I bought it lol. It's just a run of the mill tubular free float handguard with barrel nut. No markings either. Just posting here to see if anyone knows the thread sizes found on the long ARs

It might be something weird & proprietary like RRA. Large ARs don't have a design standard to conform to, so they can be vastly different depending on what you buy.
 
Ok to clarify:
You have an Aero M5/.308 upper
It came from someone second hand with a barrel nut.
Does the barrel nut fit on the receiver?
You have a handguard for an AR15?

You said the nut is too small, but you mean the diameter is fine but the thread size/pitch is off?
 
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The aero and nut are new.

The tube hg and nut I've had in the parts bin for a while. So long that I forget where it came from. It is new in wrap as well.

I was going to use the tube hg on the Aero, but the threads on the Aero are 1-7/16 and the tube hg nut is threaded quite a bit smaller.(slightly bigger than a standard AR-15 1-1/4 thread)

Based on what I'm reading on the net, manufacturers of 308 based ARs have no clue about Eli Whitney's principle of parts interchangeability. So, given the Aero upper and nut are currently married to a 6.5 Creedmoor barrel I guess I'll order a hg from Aero and toss the tube back in the parts box.
 
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