These struts are the vertical part of the ring fin assembly. They also function as guide tubes whenever the ring fin is used. Made of light, tubular polypropylene,
they have flared ends to help them glide over the gude rod during liftoff. Only three are required, and three are spares. Useful for making water rockets,
pop bottle rockets, water bottle rockets, pop bottle water rockets, water pump rockets, soda bottle rockets and bicycle pump rockets.