Invector / Standard Invector Choke Tubes. Browning was one of the original innovators in developing choke tubes designed to increase versatility of a shotgunner's barrels. Now a hunter or shooter could easily change tubes (and the pattern) without changing barrels. The original Browning Invector Choke tube system -- often called Standard Invector -- was extremely innovative for hunters and clay target shooters, allowing a fast, convenient and effective system for adjusting the pattern to the game/target and distance.
The Invector Choke Tube system utilized barrels with internal threads to screw in chokes of the shooter's choice. A wrench was supplied to facilitate removal and installation of tubes. Popular choke constrictions were offered, including Extra Full Turkey tubes and rifled chokes for deer hunting, using Sabot, slugs or heavy buckshot. This was a game-changer for the industry. Today nearly all shotguns have interchangeable choke tubes.
The original Invector (or Standard Invector) is currently found on Browning shotguns with threaded choke tubes in 10 gauge, 16 gauge, 28 gauge and .410 bore -- for primarily Citori and BPS shotguns.