What  "Flash hider" should I, or can I put on my H-Bar?    

The  muzzle OD  is  .700"  

Also.., what thread pattern??  


Thanks in advance!!!

Not all FH's have the same threads although some of them will be the same. If you decide which you want, email or call the seller and they will be able to tell you. Then Take the FH and your rifle to the Gun Shop and have them put it on. The reason I say to have them do it is because it should be done with the tool that ensures that it's put on strait. I don't think you want to buy the alignment tool as well as a Tap & Die. Some of the sets are very expensive since they are not common threads. If you do it yourself, then you will probably want to find one that is a common thread so you are not paying well over a hundred bucks for the FH and the Tap & Die.

Semper Fi

I imagine you're going to want to thread it to be able to take all standard AR15 flash suppressors.  That means you'll have to cut the end down to 1/2" diameter and thread 28 tpi (I think).  This would have to be done on a lathe.

All of the FH I have seen for the AR-15 are 1/2"x28TPI.
Even if you later want to put an AK FH on there are adapters to do so.
Have a 'smith do it on a lathe, this is next to impossible to do correctly with a die.

Yeah, have a smith do it, 1/2 x 28. Then get an A2, Vortex or Phantom to go with it.