This Nordic Components Barrel Clamp connects an extended magazine tube solidly to a shotgun's barrel, providing additional support for the tube against the added weight of additional shells enclosed within its elongated body, as well as helping to prevent the tube from being damaged and/or misaligned with the receiver if bumped, dropped or roughly handled during use. Designed to withstand the accelerated wear, tear and abuse encountered in action shooting competitions, the aluminum clamp is sized specifically for compatibility with a Nordic Components magazine tube, but will also work with any other magazine tube extension with an outside diameter of approximately 1.06". For 12 Gauge only. Notes: This clamp is for use with Mossberg 12 Gauge Shotguns. Note, this will also work with the Benelli Nova and Super Nova. For all other shotgun models equipped with a Nordic Components extended magazine tube, the correct item numbers are 185-334 (Clamp Only) or 667-570 (Clamp w/Accessory ...