The ring fins on the Star Rider are BT-80 24mm long, and the body tube is 350 mm long. BTW, for anyone who's interested in building the Star Rider, one of the Estes starter kits sold in places like Toys R Us has a rocket with the same canopy-and-canards nose cone used on the Star Rider, but molded from colored plastic; that should mean one can still special order the nose cone from Estes.