The measurements I gave are for my 42 in barrelled .54 The 5/16ths dimension is at the tip , so the rod is larger at the stock entry pipe. By the 2nd or middle pipe it's 3/8ths The pipe closest to the muzzle is slightly larger than the rest, but not noticeably so. The flare is most prominent at the 1/2 in end. My .54 has an ash rod, and that rod is over 15 years old and has seen hard use.