The SMSN0740 sphere neodymium magnet is made from high-performance N42 NdFeB, with black Nickel coating. The dimension of this item is 1/4″ diameter, with the tolerance of ±0.004″. The weight of this super strong neodymium magnet is 0.0021875 lbs. It can pull up to 1.63 lbs steel. And the surface field is up to 8815 gausses.