Strike Industries SIARARET7BK AR Advanced Receiver Extension Mil-Spec 7075 T6 Aluminum Black. AR-Style extension tube made from 7075-T6 aluminum with a black finish. Specifications: Type — Extension Tube; Model — AR Style; Size — Mil-Spec. MFG Part Number ARARET7BK; UPC 708747546118; SKU ACC-STRK-ARARET7BK. Not available to ship to California, Illinois, or Washington.