These cubes are so cool you can't put them down once you pick them up!Neodymium is a rare earth metal and it makes some of the strongest magnets possible. A single one of these tiny cubes is strong enough to be a refrigerator magnet.Each set of 64 cubes and ring comes together in a blue velvet drawstring bag.The hematite ring is also pretty cool. It's not as strong as a cube and it's not jewelry - just a magnetic ring! If it were gold, it would look just like Frodo's ring! Size range inside diameter is approximately from 16mm to 20.5 mm.  Sorry I can't honor specific sizes as they are randomly packed.Neodymium magnets are very strong. Handling them with care is necessary to prevent personal injuries, property damages and magnet damages.Normal Neodymium magnets will lose their magnetic properties if heated above 175F (80 C).The strong magnetic fields of neodymium magnets can damage items such as television, computer monitors, credit cards, bank cards, computers, diskettes and other data carriers, video tapes, mechanical watches, hearing aids, loud speakers and VCRs. Pace-makers may be damaged or switch to "Test Mode" in the presence of a strong magnetic force, if a pace-maker is in use, keep a minimum of 3 feet distance.You should avoid having constant contact with magnets of any size and keep a distance of at least 3 feet to large magnets.Children and pets should not be allowed to handle neodymium magnets as they can be dangerous. Small magnets pose a choking hazard and should never be swallowed or inserted into any part of the body.Neodymium cube Specifications:0.25 inch x 0.25 inch x 0.25 inch Neodymium Iron Boron NdFeB Cube MagnetsNickel-Copper-Nickel triple layer coated for maximum durability and protection again corrosionGrade N42Magnetized through the ThicknessApproximate pulling force: 6.6 lbs