AR 15 free float quad barrel nuts?

[woodweasel58]

I just recieved all of the parts fora new build. I want to use the 7" free float forearm from one of my JR Carbine 9mm's then replace it with a 12" forearm. The problem is the JRC 9mm is a blow back and doesn't use a gas tube. The barrel nut only has 4 holes. If I put it on my new build 1 of those 4 holes has to line up for the gas tube. I guess what I want to know is if there is anyone who knows if and which quad rails use the same barrel nut threads and which ones have proprietary barrel nut threads? Help please.

 

[jakk280rem]

Barrel nut threads are a part of the upper receiver. The barrel nut has internal threads that mate to external threads on the upper receiver. I don't know exactly what you are asking, but some ff tubes use a standard barrel nut and some use a proprietary nut. Sounds like you are planning to buy a 12" forearm anyways, when you pick one out, the manufacturer will list whether a standard nut is used or a proprietary and whether the nut is included with the forearm and what tools are needed or included.