The award winning Goblin' Thunder Choke Tube is the original extended ported shotgun choke. With the right combination of shell pellet and choke constriction Gobblin' Thunder dependably delivers a 14"-16" pattern at 40 yards. 17-4ph Stainless Steel Chemically Blackened Round Angle-ported Extension Choke Extension Is Approximately 1 1/2" Long Unique Conical / Parallel Interior Design Denser More Consistent Patterns Recoil Reduction Muzzle Jump Reduction Wrench Required Size Labeling Based On Inside Diameter Measurement