The ported brakes are a modification of the Tank brake they are ideal for competition rifles because it can be turned to match your barrel contour and will never get caught on an obstacle when changing your shooting position under time constraints. They are also great on hunting rifles because they are small light and low profile. Perfect for prone shooting. Diameter .687, minimum turn diameter .6″, threads 7/16-32 3B .  This brake needs to be installed by a qualified gunsmith.