The UTG Pro Receiver Extension Tube is a 6-position Mil-Spec diameter receiver extension tube for AR-15 rifles. It is CNC Machined from 6061-T6 Aircraft Grade Aluminum with Precisely Rolled Threads for Durable Thread Engagement with Lower Receiver. Flat Dark Earth finish. Features: Flat dark earth finish Tightest tolerance control for zero-gap fit Fits any standard AR-15 lower and a Mil-Spec diameter collapsible stock (not included)