From what it look like, you have Alot for threading before touching flit, you can have what ever thread that ate smaller than .8 and run 1/2" toward the action, this aloe you to have about .125 before thread hit the flute, there is Alot to work with, clam on are no good, for clam on to work, the lenth of the area you need to clam on must not be taper, clam on will result in vibration, causing the muzzle brake to come off, or twisted.