Manufactured from high strength steel and finished in a nickel-alloy coating, these chokes guarantee significant corrosion resistance and have the ability to withstand the rigors of steel shot; Optima-Choke HP 20 ga tubes are fully interchangeable on all Beretta barrels that are threaded for Optima-Choke HP (the Optima-Choke HP choke tubes are not interchangeable nor usable with barrels designed for the Optima-Choke system); A choke system locating the threaded portion of tube a nominal 10 mm (.394 inch) further to the rear of the muzzle end of the tube than found on the Optima-Choke system; Increased wall thickness at the muzzle end of the choke tube where the greatest degree of choke constriction typically occurs and stresses are the highest without having to use the larger barrel contour; Every Beretta choke tube has information engraved on the tube to identify the manufacturer (PB), the constriction (F, IM, M, IC, CYL), the approval for steel shot use (SP) and the choke type (Optima-Choke, Optima-Choke Plus, Optima-Choke