N, M, H, SH, UH or EH indicate the maximum working temperature of a magnet.
Most of our magnets begin with the letter "N" and can thus withstand temperatures of up to 80 °C.
You can find out which letter corresponds to which maximum working temperature under FAQ "What temperatures can magnets withstand?
(e.g., 40, 42, 45) are equivalent to approximately the maximum energy product
of the magnet (in MGOe).
They are an indicator of magnet strength.
According to the current state of the art, the grade 52 corresponds to the largest possible maximum energy product of a permanent magnet.
You can find the exact correlations between these classifications and the physical values of a magnet in the table Physical magnet data