It was originally a 5 1/2" flash-hider from an AR. I was re-configuring my AR to a free-float tube and had to remove the permanently attached flash-hider. This destroyed the threaded portion so I cut an inch off of it. I then drilled and tapped two holes on the bottom for the set screws.
I tried some cold blue to touch it up but as you can see in the pics it turned out too light. Today I removed it and gave it a coat of flat black.