Browning Invector-DS choke tubes have a double seal which keeps tubes cleaner. The longer choke tapers are optimized to percentages, not just dimension. The proprietary differential banded gas seal eliminates residue build up and makes chokes easy to remove and install. Integrated spring suspension holds the seal tight while allowing expansion and controlling gas. *Note- Invector-DS tubes fit only Browning shotguns designed for Invector-DS and are not for use in shotguns showing Invector-Plus or Standard Invector on the barrel.