The UTG Pro Mil-spec 6 position diameter receiver extension tube for AR15 rifles. The extension tube is CNC machined from 6061-T6 aircraft grade aluminum with precisely rolled threads for durable thread engagement with the lower receiver. Finished in a matte black Type III Class II hard coat anodized. Proudly designed and made in USA Features: 6-position Mil-Spec diameter receiver extension tube for AR15 rifles Extension tube CNC machined from 6061 T6 aircraft grade aluminum with precisely rolled threads for durable thread engagement with lower receiver Underwent the tightest tolerance controls for a secure fit and function with various collapsible stocks Finished in a matte black type III class II hardcoat anodize Proudly designed and made in USA