These precision rifled choke tubes are made of high-strength 304 stainless steel. Each choke tube protrudes 0.625 to 1.3 inches from the end of the barrel, depending on the type of firearm for which the choke tube was specifically designed. Each choke tube has a right-hand rifle twist, which is 1 to 35. Each choke tube has a groove diameter of 0.730 inch in 20 ga. These throttle tubes have a matte black finish and come with a lifetime warranty. If you're looking for improved accuracy from a smooth-bore barrel, these slim choke tubes will enhance your groups.