Sonic-Tronics Servo Arms. 8 arms per package for JR, Cox & Sanwa Servos. Injection Molded from engineered composite materials containing long carbon fibers. This combination of materials bring the modeler a super performance product. They are larger, stronger and more rigid than any other standard servo arm available. When models are powered by 90, 120 or larger engines or are 1/4 and 1/3 size, higher performance products are a required item for safety. Two Versions available. The 8 pack has two each of four types, two double arms, two each of the small, medium, and large single servo arm. The 4 pack has one each of four types. One "X" arm, double arm, and one each of small and medium single arm.