Nordic Components MXT Magazine Extension Nut, Combines with MXT Tubes to Form Complete Extension Kit, Compatible with Remington 870, 1100, 11-87, Versa Max, and V3 NUT-RM-12-00 The MXT extension 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.