Apachejoe

I have a Rock River Arms AR10? LAR8? 16", Thought I'd put a Low Profile gas block and slim clamp on forearm and man! I cant find a forearm with the right treads. Don't know the different patterns and also purchased a tubular 12" from RRA,then the barrel nut is made in the dang thing so, cant use the low profile gas block and gas tube unless there is some voodoo to get the gas block on after the forearm and gas tube is in place! all I wanted to do was change out the Factory forearm to a slim 12" clamp on and now its a guessing game or gamble if I buy a Forearm with the right thread pattern !!! any help would be great!!/anyone!!

Hey everyone! my question is , I just Purchased a RRA LAR 8 Lower and was fixx'n to to go with Armalite upper but, after doin sum read'n now I'm confuzed on what upper to try cause some folk say they will not fit. I have probally built a couple dozen 15's an 16's but am new to the AR10 or LAR style 308/nato, have built some FAL's n CETME's but sorta new to this platform! thanks in advance for anyones input. Apachejoe