Pattern Plus Choke Tube, Improved Modified The Pattern Plus style choke tubes fit flush with the end of the barrel. They are manufactured from high strength 17-4 PH stainless steel and are marked on the body with the degree of choke as well as the exit diameter. They are the choice for those shooters who want a high quality choke tube but prefer a flush mount style. Fits: LC Smith 20 Gauge Flush Mount Constriction: .603