Carlson's 12 Gauge Browning Invector DS Sporting Clays Choke Tube, Skeet - 18852. These Carlson Sporting clay choke tubes are constructed from 17-4 stainless steel. They are precision machined to ensure they produce a better pattern vs standard choke tubes. The tubes features a 25% larger parallel section throwing more consistent patterns. Each tube has a knurled end to allow for quick removal and they are individually laser marked with their constriction type for easy reference.