Standard invector tubes produce patterns with excellent uniform densities. It is set to industry constriction standards and are made of 17-4 stainless steel. Standard Invector choke tubes fit only Browning shotguns designed for Standard Invector and are NOT for use in shotguns showing Invector-Plus or Invector-DS on the barrel(s). Type Flush Gauge 20 Gauge Finish Stainless Ported No Material 17-4 Stainless Steel Configuration Invector Chokes Included 1 Recommended For 20 yds Constriction Type Cylinder Constrictiondiameter .000