These race cars can be used with other SmartMax race track sets. 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. SmartMax is carefully designed to meet and exceed the world’s toughest safety requirements, including giant-sized, non-swallowable 1.8” diameter metal balls and inaccessible magnets encased in specially sonic-welded bars.