If I am remembering the code correctly if the barrel is threaded than it cannot be placed on a post ban rifle. You would than in theory have to permanently affix the break to the barrel. I would lean against this due to the fact that the ban may expire in 2004. Than all this is pointless anyway. You could do it anyway if you like the brake that much. But you would still have to have it permanently affixed. I think Bushmaster welds as well as pins their brakes.

You may thread on a muzzle brake then high-temperture silver solder or spot weld it on (they do NOT silver solder a set screw - they use silver solder directly on the threads).  The BATF consideres this 'permanent' like pinning & welding on a brake on a non threaded barrel.  By permanently attaching the muzzle brake in this manner, the thread are effectivly 'eliminated'.