Nordic Components
Universal 12-gauge MXT +2 tube, cap, and spring kit; an M2 installation still requires the separate NUT-BN-12-00.

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Nordic Components MXT Magazine Extension Kit +2 For 12GA Shotguns - MXT-TBS-12-2
The MXT-TBS-12-2 is Nordic's universal 12-gauge +2 tube kit. It includes the extension tube, tube cap, and full-length spring, and its capacity figure is based on 2.75-inch star-crimped shells. It does not attach to a Benelli M2 by itself: the M2 requires Nordic nut NUT-BN-12-00. Shell length and the host's factory tube determine the final loaded count. Nordic's fit guide points 18.5-inch M1/M2 owners to the longer +3 or flush +3B geometry, so this +2 remains a valid compact tube option rather than the guide's complete Tactical bundle.
Add the Nordic Components MXT +2 Benelli M2 Extension to your build and see how it enhances your platform.