Here is what SilencerCo said (cobbled together over a few emails) regarding using a device to attach my Omega can on my .63 diameter barrel:
We would recommend the 9/16x24 thread pitch. However, we would recommend going with the RH thread and using the muzzle brake. All of our tests have shown that the muzzle brake has better accuracy than the flash hider. If you are worried about the side concussion then you can use the ASR Blast shield to direct the blast forward. The 9/16x24 will give you enough shoulder for proper shouldering of a flash hider or muzzle brake.
