15x10x3 mm (N35) Neodymium Magnet. Grade: N35. Neodymium is about as common as tin or lead. There are two types of “Rare Earth Magnets” SMCO (Samarium-Cobalt) and Neodymium. Neodymium are the magnetically stronger and cheaper of the two but are more susceptible to oxidation, this is why they are protected by Nickel plating.
eBay