With magnetic connectors and steel spheres, your students can easily build tetrahedrons, cubes as well as an endless array of other structures. Each kit contains 100 super strong Neodymium magnetic cylinders (5 mm DIA x 13 mm long, N38 magnets) and 50 small steel spheres (10 mm DIA). Honestly, this kit is worth purchasing just for the 13 mm neodymium rods... We love it!Note: All Rare Earth magnets, such as neodymium magnets, are made of a ceramic and can be brittle. They are extremely strong magnetically must be handled with caution to avoid damage to the magnets and/or injury. Fingers can be pinched between attracting magnets and magnets can chip or break if allowed to 'jump' at an attracting surface or another magnet. Adult supervision is required.