Rare earth magnets are the strongest type of permanent magnet currently made. They are amazingly powerful for their size and have innumerable uses. These cylinder magnets are 0.250 inch (6.4mm) outside diameter, 0.100 inch (2.54mm) inside diameter and 0.250 inch (6.4mm) long. They are magnetized through the diameter. They are composed of grade 40 neodymium iron boron magnetic material and are plated in nickel-copper-nickel for a shiny corrosion resistant finish. Maximum working temperature is 176 F (80 C).