Carlson's Choke Tubes Cremator Ported Waterfowl Retay Choke Tube Mid-Range Black. 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. Specifications for Carlson's Choke Tubes Cremator Ported Waterfowl Retay Choke Tube: Manufacturer: Carlson's Choke Tubes Fabric/Material: 17-4 Stainless Steel Choke Tube System: Retay Choke Carlson's Choke Tubes 11583 Cremator Close Range Retay Ported 17-4 Stainless St Carlson's Choke Tubes 11585: Cremator Ported Waterfowl Retay Choke Tube Mid-Range Black