Beretta Choke Tube Optima-Choke Light- Modified Flush in 12Ga. Fits Beretta 682, Some 687 models, Silver Hawk, DT10, Some 391 models These Optima Choke tubes are available in internal and external versions for 12 gauge shotguns. They are longer and slimmer than conventional Mobilchoke tubes. Thanks to the elongated cone they minimize pellet deformation and improve shot patterns. The various versions are fully interchangeable on 12 gauge guns with Optima Bore barrels. These choke tubes are for 12 gauge shotguns with the Optima-Choke system only. How to Identify In the year 2000 Beretta introduced the 12-gauge Optima Bore barrel design into some of their competition shotguns. This new barrel utilized a larger internal bore dimension known to some as “back-boring” and required a new choke tube design to give the proper constrictions. The Optima barrels can be identified by locating the letters “OB” stamped next to the barrel gauge stamp. Barrels marked with the "OB" stamp will use the Optima-Choke system. This design features a longer internal transition taper into the choke constriction, making the overall length of this tube longer than the original Mobilchoke tube. Identifying Characteristics: Barrels that use the Optima-Choke will typically be marked OB immediately adjacent to the gauge marking. Optima-Choke choke tubes will be marked Optima-Choke. The start of the threaded portion of the Optima-Choke tube is located a nominal 50.78 mm (2.00 inch) from the breech end of the choke tube. The length of the threaded portion is a nominal 15.9 mm (.625 inch). The major diameter of the choke tube thread is 20 mm (.787 inch). The Optima-Bore/Optima-Choke system is typically used on competition 391 series semi-automatic, 680 series over and under shotguns and UGB25 Trap models.