Magnetic STEM Building Fun! Have fun building incredible structures with SmartMax! The oversized pieces are specifically designed for handling by young kids as they learn about the effects of magnetic attraction and repulsion, while older children will have fun using the pieces to construct towers, bridges and other creations. The Start XL set includes 18 short magnetic bars, 12 long magnetic bars, 12 magnetic balls and a guide to build models. Extension sets are available separately.