Rare Earth magnets are the strongest type of permanent magnet currently made. They are amazingly powerful for their size and have innumerable uses. These countersunk ring magnets are 3/4 inch diameter x 1/5 inch inside diameter x 1/8 inch thick. They are magnetized through the thickness. They are composed of grade forty neodymium iron boron magnetic material and are plated in nickel-copper-nickel for a shiny corrosion resistant finish. Maximum working temperature is 176° Fahrenheit. Magnets may chip and crack if allowed to snap together. WARNING: Keep out of reach of children. This is NOT a toy. Secure magnets when unattended. Ingestion and inhalation hazard. Ingestion or inhalation may cause injury or death. Seek immediate medical attention if magnets are swallowed or inhaled. Keep magnets in this container when not in use. May affect internal medical devices such as pacemakers. Keep away from internal medical devices. Magnets are brittle. Broken magnets are sharp. May break or ignite if drilled or machined. Do not burn, drill or machine. Magnetic media and electronics hazard. Magnetic material is regulated for air transport. This product does not exceed USDOT and IATA field strength limits as originally packaged.