Rob Roberts Gun Works T1 Triple Threat Mobil 20 Gauge 17-4 PH Stainless. Provides a wide but uniform pattern to cover fast moving targets. These choke tubes are built from years of product development and innovations using the highest advanced technology available. They are made out of 17-4 PH U.S. Stainless Steel. Specifications for Rob Roberts Gun Works 200112 T1 Triple Threat Mobil 20 Gauge 17-4 PH Stainless S: Manufacturer: Rob Roberts Gun Works Fabric/Material: 17-4 PH Stainless Steel Gauge: 20 Choke Tube System: Beretta/Benelli Mobil Rob Roberts Gun Works 200112 T1 Triple Threat Mobil 20 Gauge 17-4 PH Stainless