Carlson's Super Steel Shot Choke Tubes -The longer parallel section allows for use of larger steel shot in tighter choke constrictions. They are made of 17-4 stainless with a knurled extension and a blue finish. Each choke tube carries a lifetime warranty. All steel shot sizes may be used in the close and mid-range choke tubes. Do not use steel faster than 1550 FPS or steel shot sizes larger than BB through the Long Range choke tube. Do not use steel faster than 1550 FPS or steel shot sizes larger than BB through the Long Range choke tubeThey are made of 17-4 stainless with a knurled extension and a blue finish