the Spikes ET-1 can (threaded 1/2X28) is a screw on length adding item. 1 1/4'' diameter X 6'' long. It ADDS the length to to your barrel. So the outside diameter of the thread adapter would be immaterial. A reverse flash suppressor hides 3'' of the barrel length, one without holes sure looks a lot like a can. The thread adapter must be turned down a little to fit inside the suppresor. A drill, a file and a bolt and nut to use as an arbor is simple and works well. DPMS sells a nice one pretty cheap.