Neodymium magnetic sphere magnetic cube Magnetic balls, sizes can be customized. Size range: 2mm-50mm. Material:Neodymium N35 (Work temp Coating:Nickel, Black Nickel, Silver, Gold. Color:Red, Black, White, Orange, Yellow, Blue, Light Blue, Purple, Rainbow, etc. Warning:1. Donât swallow. This product contains small magnet, swallowed magnets can stick together across intestines causing serious or fatal injury. Seek immediate medical attention if magnets are swallowed or inhaled. 2. These are so super strong, they should be kept away from children.