Carlson's 20 Gauge Cylinder Flush-Mount Choke Tube, Invector The Carlson's Cylinder Choke Tube is a 20 gauge shotgun accessory with a flush-mount design and Invector interface. Cylinder identifies the choke configuration, while the gauge and interface identify the type of barrel system the accessory is intended to match. A flush-mount choke sits within the muzzle profile instead of extending beyond it. The Invector designation is a fitting-system detail, so it matters separately from the 20 gauge specification. Together, gauge, choke configuration and interface provide useful selection details without implying that the tube fits every shotgun from a particular brand or every Invector-named system. Key Features 20 gauge: The gauge specification for this choke tube. Cylinder configuration: The cylinder choke configuration. Flush mount: A design that sits within the muzzle profile. Invector interface: The fitting-system designation supplied for the tube. Specifications Manufacturer: Carlsons Brand: Carlson's Gauge: 20 gauge Choke configuration: Cylinder Mount style: Flush mount Interface: Invector Product type: Choke tube Shop the Carlson's 20 Gauge Cylinder Flush-Mount Choke Tube, Invector at BattleHawk Armory.