Launch more marbles! With the spinner up to six balls can be started at once. Watch as the marbles are sent on a race through your tracks. This extension allows you to build up to six different track courses. Combined with the Starter-Set, you could have up to nine different tracks launched at once. How many marbles will you race? This STEM system [Science, Technology, Engineering and Maths] is an ideal one to teach kids about gravity, magnetism, kinetic energy and fun. Hit a snag? Freestyle with your own track design or use the tasks and blueprints included to help you to get started in the world of GraviTrax! Are the gravity spheres stopping or flying off before reaching the end target? Time for some problem solving. Rebuild and try something different! The GraviTrax track system can be extended indefinitely with extra track packs and add-on's – each sold separately.