BLACKHAWK! Mossberg 500 Swivel Set Threaded lock-down plunger with knurled, all-steel plunger knob for maximum performance All steel construction for ultimate ruggedness and durability Finished to match fine blued or stainless firearms Mounts on magazine tubes 630 to 675 diameter Lock-down swivel set Fits the Mossberg 500 LOK-DOWN swivel set Includes replacement takedown screw with swivel base Wood screw rear base One inch blued