Longer parallel section than Carlson's conventional tubes gives consistent shot patterns. Extra smooth interior surface minimizes shot deformation. Laser marked constriction provides fast identification. External knurled ring extends approximately 3/4" from end of barrel for fast changes between stations. Can be used with steel shot. Mfg: Carlsons SPECS: 1704 stainless steel. Constriction (SIZE). Threads are as follows - Beretta - 12 ga., plus Benelli M1 and Super 90, 12 ga., .810"- 1mm.