Carlson's Rifled Choke Tubes are an extended tube, designed to protect the end of the barrel while stabilizing the slug for enhanced accuracy. Manufactured from 304 high stress stainless steel, these tubes are designed to work with traditional slugs as well as rifled slugs and sabots. Carlson rifled choke tubes feature a right hand, 1 in 35" twist rate which will improve your groups from a smoothbore shotgun barrel. Matte black stainless steel will resist corrosion. Choke tubes carry a lifetime warranty. Notes:Each choke tube has a groove diameter of .730 of an inch in 12 ga.Each choke tube has a groove diameter of .620 of an inch in 20 ga.