Milspec Lightweight aircraft aluminum.

Hi John, he LBE Unlimited Mil-Spec AR-15 Buffer Tube is an easy-to-install 6-position buffer tube, engineered to deliver unparalleled strength and consistent performance with most Mil-Spec receivers and buffer systems. Lightweight aircraft aluminum construction ensures lasting strength and stability, while the corrosion-resistant anodized finish protects against rust, scratches, and other damages. Plus, this buffer tube is 100% American-made using top-shelf materials and precision machining for superior quality.
Stay safe & have a great day!

Hi John and welcome. This is an Aluminum Mil-Spec Diameter Buffer Tube. Cheers and stay safe!