I would guess the barrel has to be the right diameter to begin with?
In order to thread your barrel to 14mm to accomodate these brakes your barrel must be about 0.52" - 0.58" O.D. This diameter barrel is common among military AKs and SKSs.
What threads? I can order a die. I already have 1/2-28, M9X0.75(SIG Mosquito), and a few others.
If you don't have a factory threaded barrel then your barrel can be modified, extended, and threaded.Derf, could you elaborate on the sig mosquito barrel threading? I have one, and would like for it to be threaded, would this basically be like the P22 barrel, and need an adapter?