Carlson's Rifled Choke Tubes, 12 and 20 Gauge are manufactured from 304 high stress stainless steel. Each of these Choke Tubes made by Carlson's Choke Tubes protrudes .625 to 1.3 inches from the end of the barrel depending upon which type of firearm the choke tube has been specifically designed for. Each Carlson's 12 & 20 Gauge Rifled Choke Tube has a right hand rifle twist, which is 1 to 35. Each of these Carlson's Shotgun Choke Tubes has a groove diameter of .730 of an inch in 12 ga. The Rifled 12 and 20 Gauge Choke Tubes by Carlson's have a matte black finish. If you're looking for improved accuracy from a smooth bore barrel, Carlson's Choke Tubes are guaranteed to improve your shot groupings.