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 - Browning Invector-Plus - 12 ga., .820"-32.