GraviTrax Loop $12.99 Default Title - $12.99 Quantity This product is currently sold out. Please fill in the form below if you'd like to be notified when it becomes available! Turn the marble upside down with the Loop accessory. Experiment with how much speed the marble needs to loop-the-loop. This accessory also includes 6 additional tracks. GraviTrax Starter-Set required. Recommended for children ages 8-99.