Manufactured from 17-4 heat treated stainless steel. These chokes may be used with lead shot on any constrictions. Steel shot larger than #BB should not be used in any choke tighter than full.Specifications:- Gauge: 20- Type: Flush- Choke: Improved Modified- Constriction: .595Fits: Remington 20 ga. Choke Systems.20 GA FLUSH MOUNT(This Product does not fit the Remington Pro Bore or the Remington Spartan Models)