Named 2010 Toy of the Year when it was first introduced in the Netherlands, SmartMax is the magnetic discovery concept that allows children, even from a very early age, to experience both the wonders of magnetism and the fascinating world of construction in a safe way. The extra-large pieces make it easy for small children to manipulate them. The magnets have the ideal strength for easy assembly and breakdown of constructions. Outstanding, colorfully-illustrated guides in each set demonstrate the basics of magnetic phenomena, ways to strengthen structures, steps in building towers and bridges, and much more. Most importantly, children thrive on the creative satisfaction of dreaming up their own wonderfully imaginative magnetic assemblies. This product includes 6 extra balls. Balls measure 1.75" diameter.