The Leapers UTG PRO US Made Mil-Spec 6-Position Receiver Extension Tube was manufactured to Mil-Spec diameter specifically for use with AR-15 style rifles. This extension tube features the tightest tolerance control and a secure fit that is guaranteed to meet even the most demanding needs of serious silent operators.The Leapers UTG PRO US Made Mil-Spec 6-Position Receiver Extension Tube is crafted using 6061 T6 aircraft-grade aluminum with a hard-anodized finish to ensure a lifetime of durability. Additionally this six-position receiver extension tube is proudly made in the USA.