The JAG Arms Barrel Nut Adapter for M-Lok Rail Systems. A must-have for those installing a new handguard M-Lok on your airsoft gun. Fits all standard M4 airsoft AEG style guns, with the Tokyo Marui system. Works with the SLM Jag Arms 9, 13, and 15 inch M-Lok handguards. Uses a standard barrel nut wrench for installation.