O.D. Spec as in Out Door Gear Specifically used for camping outdoors. While O. D. is typically tossed around in our shop as “Outside Diameter”, the “builds” are all in pursuit of enjoying the outdoors provided by mother earth, of which has an outside diameter (O.D.) of 24,860-miles (40,008 km) around the equator, according to NASA’s Goddard Space Flight Center in Greenbelt, Maryland. We are in Colorado Springs – GO EXPLORE!