Iver Johnson Arms Iver Johnson Choke Tube 12ga. Rifled Mobil Choke Extended. Manufactured from a premium quality steel that has been case hardened and then heat treated the Iver Johnson Rifled Mobil choke tubes provide long life and excellent patterning. Iver Johnson Rifled Mobil choke tubes use patented sonic welded joints that are far superior to any other manufacturer. These choke tubes are designed for use with lead shot in all constricted States. You must remove the safety pin before installing this choke tube. Iver Johnson does not warrant these choke tubes for loss of pelt or damage to hull or choke tube. Specifications for Iver Johnson Arms Iver Johnson Choke Tube 12ga. Rifled Mobil Choke Extended: Manufacturer: Iver Johnson Arms Color: Black Fabric/Material: Steel Gauge: 12 Choke Tube System: Mobil Choke Choke Type: Rifled Gun Make: Iver Johnson Package Contents: Iver Johnson Arms Iver Johnson Choke Tube 12ga. Rifled Mobil Choke Extended