Carlson's Delta Waterfowl 20ga Choke Tubes are manufactured from 17-4 stainless steel and are designed to throw tighter and denser patterns than conventional choke tubes. These choke tubes feature a 25 percent longer parallel section in the choke, thus throwing more consistent patterns. Each choke tube is knurled on the end to allow for quick and easy removal and has the constriction and type laser marked on the end and body for easy reference. steel shot may be used through these choke tubes with exceptional results. Do not shoot steel shot larger than bb or any steel load faster than 1550 fps through the long range constriction. Loads that exceed this size and speed should be used with the mid range choke tube. This choke tube is for close range and fits Browning Invector Plus models.