This 2-5/8" plastic servo wheel (Black) fits on standard Futaba servos and has a diameter of 2-5/8". Each wheel has a silicone tire and 64-stripe encoder pattern molded in. The Solarbotics SW wheel is compatible with standard Futaba servo hubs such as those on the SpringRC SM-S4303R continuous rotation servo. The plastic wheel is molded from ABS and has a molded-on thermoplastic silicone tire with great traction and wear characteristics. There is a 64-strip encoder pattern on one side of the wheel compatible with the Wheel Watcher. The plastic wheels measure just under 2-5/8" (69 mm) across by 0.3" (7.62 mm) wide.