This is a replacement wheel (with rubber-band tire) for use in small robot kits, such as the Boe-Bot, SumoBot or Arduino Robotics Shield Kit.
In case one should break, a second rubber band is included.
The 2.62" (66.5 mm) diameter molded plastic wheel fits on a Parallax continuous rotation servo spline, or on Futaba and GWS servos. It does not fit Hitech servos. The holes in the wheel are designed to work with the Digital Encoder Kit for Boe-Bot.