TST is a series of three graduated rings in the taper section of the choke tube that allows a more gradual transition from the shotgun bore to the final constriction. This design offers reduced pellet deformation, less flyers and more dense patterns. These benefits make the Cremator® Series extremely effective on all types of waterfowl throughout the entire season. The Cremator® series has no size or speed restrictions with steel shot in any of the three constrictions. You also get all the benefits of an extended choke tube, including a 25% longer parallel section for tighter and more dense patterns, wrench-less installation, quick removal and helps with muzzle protection.