Carlson's Flush Mount Extra Full Turkey Choke Tube, Fits 12 Gauge Mossberg 835 or 935 Shotguns .680 Constriction Manufactured from 17-4 stainless steel and hardened. For use with lead shot in all constrictions. Steel shot larger than #BB should not be used in any choke tighter than modified, BB and smaller size steel shot may be used through full choke constriction Not for use with steel shot