Crio/Crio Plus--These precision Rifled Choke Tubes are manufactured from 304 high stress stainless steel. Each choke tube 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 choke tube has a right hand rifle twist, which is 1 to 35. Each choke tube has a groove diameter of .620 of an inch in 20 ga. These choke tubes have a matte black finish and carry a lifetime warranty. If you're looking for improved accuracy from a smooth bore barrel these fine choke tubes will improve your groups.