I know what a single piece FFT is, but can someone explain to me exactly how a two piece FFT goes together? I am looking at the model 1 tube to put on an upper I am building. The barrel is going to be of the 16" variety with a low profile gas block. I want to put a rifle (read 20") tube on the upper to hide the gas block. Does a two piece tube come with barrel nut that goes on first, then the gas block and tube, and finally allows the FFT to screw on over the whole barrel?  Any help would be greatly appreciated.
(links to pics too!!)

tmix

Yes, I just went through something similar myself just yesterday... shoulda taken pictures. The 2-piece FF tube from Model 1 comprises (1) a barrel nut, with holes to engage the barrel wrench and fine male threads to screw on the tube, and (2) the tube itself, which has fine female threads where it attaches to the barrel nut.

To install the FF tube, you may still have to remove the gas block if the nut/tube will not clear it. In any case, the procedure is to insert the barrel into the upper receiver in the normal way, then apply some moly grease to the receiver threads and thread on the barrel nut (see sticky at the top of this page for torquing and alignment advice). Next, you thread on the tube itself (I did this just hand tight with a SMALL drop of blue Loctite). Lastly, you reinstall the gas block (if removed) and muzzle device.

If you are using iron sights, I suggest you check that the front sight is straight before locking everything down... its a pig to fix later. Good luck, and IM me if you have any more questions.

Perfect! That is exactly what I needed to know! Do you happen to know what the I.D. of the FFT is?

Quoted: Perfect! That is exactly what I needed to know! Do you happen to know what the I.D. of the FFT is?

My 20" Model 1 FF tube has an ID of 1.8". Remember, though, that the gas block will probably have to be much less than 1.8" at its widest point, as most are asymmetric (bigger above the barrel than below).

according to my calculations, I should have plenty of room to play with.
Thanks very much!

tmix