WHAM-O HDX Model Flying Disc Frisbee, Red The Super Flex Fastback has the same great flight of the standard Fastback, however, it is softer and works great in cold weather. U-Max, HDX, Ultraviolet and Cypher are 10 7/8"D, Fastbacks are 9 5/6"D and Ring is 11 1/2"D. Ultraviolet model changes color from clear to purple, red, orange or yellow when exposed to UV light.