This is a tennis ball holder that can be screwed on any bicycle that has drill holes for a bottle holder. Tired of not knowing how to transport a tennis ball with the bike? Here's the final solution. Does't matter if you simply want to have a ball handy when going out with the dog (like me) or if you play bike-tennis or are a professional tennis ball forwarding company. The tennis ball holder can also be mounted on cars, hovercrafts and tanks - if you don't have a bicycle.