Here is another source. this one is the "clam" style. he does them in thread on, clamp on. stainless, mild steal. different sizes etc. Some of the guys over in the bmg section of the ar forum have expressed that this is a good break. i have thought of changing the fish gill off my edm and put one of these on.
My suggestion for the "gill" brakes over the "clam" brakes are that depending on what stock the rifle is going to use the clams cause slight problems with pushing the cheek piece up into the shooter upon firing.