Their Waterfowl Extended Choke Tubes are manufactured from 1704 stainless steel and designed to throw tighter and denser patterns than conventional choke tubes. These choke tubes feature a 25% 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. Each choke tube has the constriction and size 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 BBB or any steel load faster than 1550 FPS through the Full or Extra Full Constrictions. Slugs, sabots, and rifled slugs are not to be used in any choke constriction tighter than Improved Cylinder. Remember to pattern your shotgun choke tube with the specific shotshell load you are going to be using. Different brands of ammunition throw different patterns from the same choke tube.