The UTG Mil-Spec Receiver Extension Tube Kit is made from 6061-T6 aluminum with rolled threads and a matte black hard coat anodized finish. Included is a 6 position extension tube, carbine buffer, buffer spring, receiver end plate, and a castle nut. Made in the 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