UTG UTG Pro PRO Mil-spec 6-position Receiver Extension Tube is 922R compliant. This UTG Pro gun part is precision machine made from 6061/T6 aircraft grade aluminum. UTG's PRO 6-Position Extension Tube provides the tightest tolerance control for a zero-gap fit with polymer stock and receiver. Built for the most serious user, UTG Pro Extension Tube is designed to meet the most demanding silent operations. Specifications for UTG Pro AR308 6-position Receiver Extension Tube: Manufacturer: UTG Pro Color: Black Finish: Matte Fabric/Material: Aircraft Grade Aluminum Gun Make: AR Platform Gun Model: AR308 Projectile Caliber: .308 Caliber Country of Origin: USA Caliber: .308 Winchester Features of UTG Pro 6-Position Extension Tube: 6-position receiver extension tube with Mil-spec diameter for .308 AR Rifles Matte Black Anodizing with Mil-spec, Type III Hardcoat, Class II 922R Compliant Package Contents: UTG Pro AR308 6-position Receiver Extension Tube