"TruC 12ga IM Choke Tube Description Tru-Choke Shotgun Choke Tubes are stainless and steel shot compatible through full choke construction. Special order chokes and choke systems added to barrels use this Tru-Choke System. All small diameter 12 ga. chokes are available in stainless steel and may not be used with steel shot. This choke system is usually installed in barrels with outside diameters of .805 to .825, and is designed to be shot with 2 3/4"" lead loads only. - 12 Gauge - Improved Modified - .705 Constriction"