The Nordic Components' Magazine Extension Tube Nut allows for installation of a Nordic Components MXT 12ga shotgun extension tube kit. The nut replaces the factory magazine cap, and is required for installation of the extension tube kit. The SX-model nut is compatible with the following 12 gauge shotguns: Winchester SX2, SX3, and SX4, FN SLP and SLP Mk. 1Browning Gold - nothing longer than +4, and Browning Silver. Any magazine dimples or spring retaining devices will need to be smoothed or removed to allow proper function.NoteThis nut will also be compatible with other shotguns utilizing the same factory magazine thread pattern, but may require modification/fabrication for proper installation. Nordic Components does not have specific information regarding compatibility beyond the models listed in this description.