The Winchester Invector-Plus interchangeable choke tube system works hand-in-hand with back-boring to offer consistent, dense shot patterns with just the constriction needed for the shooting situation. The longer choke taper inside an Invector-Plus choke tube produces consistent patterns with more uniform densities and fewer fliers. Invector-Plus eliminates gases slipping between the choke tube and barrel that could damage the choke tube and the barrel. Type Flush Gauge 12 Gauge Finish Black Ported No Series Choke Tube Material 17-4 Stainless Steel Configuration Invector-Plus Chokes Included 1 Recommended For 40+ yds Constriction Type Full Constrictiondiameter .030