42H grade magnet refers to a neodymium-iron-boron magnet that can operate normally at temperatures below 120°C. In practical applications and testing, some people may wonder why the surface magnetic field of a 42H magnet can still be measured to be above 500mT (5000 Gauss). Isn't it supposed to be around 4200 Gauss at most?
In fact, this phenomenon is not abnormal. Asking this question is due to insufficient understanding of the relationship between magnet grades and surface magnetism.
Firstly, the "H" in 42H represents high coercivity, mainly improving anti demagnetization ability and temperature resistance, without significantly reducing residual magnetism. It is not much different from ordinary N42, and under reasonable structural size conditions, 42H fully possesses the magnetic properties to achieve surface magnetism above 500mT.
Rectangular neodymium magnets with 2 countersunk holes

The surface magnetic flux density is not only related to the material grade, but also affected by the thickness of the magnet. Even if it is not the highest grade, as long as the thickness is sufficient, the surface magnetic flux value can still be very high. For example, a cylindrical magnet of N42 grade Ø 15 × 25mm has a significant magnetic flux concentration effect due to its axial thickness of 25mm. The measured surface magnetic flux can reach about 5450 Gauss (≈ 545mT). Another example is a rectangular block magnet of N42M grade 9 × 12 × 12mm, which can also measure 5010 Gauss (≈ 501mT) under a thickness of 9mm.
So, a 42H magnet with a magnetic field exceeding 500mT is a conditional and normal phenomenon. Ordinary 3mm and 5mm thick magnets cannot achieve such high surface magnetic strength.
Introduction to 5000 Gauss Magnet;
How strong is a 5000 gauss magnet?
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