A grade such as N42SH has two parts, and each answers a different question. The number is the nominal maximum energy product, (BH)max, in MGOe [1], [2]. The letters give a class of intrinsic coercivity (Hcj), the material's resistance to being demagnetized [2], which suppliers turn into a maximum working temperature [1], [4]. Neither part is a pull-force rating, and neither is a guarantee for your application.
What the number tells you
N42 means a nominal (BH)max of about 42 MGOe, roughly 334 kJ/m³; one supplier's datasheet lists 334 kJ/m³ as the typical value [3]. It describes how much magnetic energy the material can deliver, so a higher number means a stronger material. It does not say how hard a particular magnet will pull, because pull force also depends on size, shape, the air gap and what the magnet touches (see why the datasheet pull force is not the force you get). Values for the same grade differ a little between suppliers, and even between tables on one page: one supplier lists N42 at 13,150 G and 42 MGOe and N42SH at 13,100 G and 41 MGOe in one table, and both at 12,800 G and 42 MGOe in another [1]. Treat the grade as a class, and ask for the datasheet of the material you are actually buying.
What the letters tell you
The letters stand for a minimum intrinsic coercivity. One manufacturer's guide gives these minimums: no letter, 12 kOe; M, 14 kOe; H, 17 kOe; SH, 20 kOe; UH, 25 kOe; EH, 30 kOe; AH, 35 kOe [2]. Supplier tables turn the classes into reference working temperatures: 80 °C for no letter, 100 °C for M, 120 °C for H, 150 °C for SH, 180 °C for UH, 200 °C for EH and 220–230 °C for AH [1], [4]. The AH figure differs between tables, and some suppliers list N52 lower, at 60–70 °C [1], [3].
Why the temperature figure is only a starting point
These temperatures are reference values, not limits you can read off for every part. One supplier states that the maximum working temperature depends on the circuit in which the magnet operates, that its figure applies at a length-to-diameter ratio of 0.7, and that customers should consult the manufacturer for applications near 150 °C [3]. Another notes that size and shape also affect performance at high temperature [4]. In general, a thin disc magnetized through its thickness works at a lower permeance than a long cylinder, and can lose strength permanently at a lower temperature than the same grade in a longer shape.
Heat also shrinks the margin itself. For grade N35, one manufacturer lists reversible temperature coefficients of about −0.12 %/°C for Br and −0.618 %/°C for Hcj, measured between 20 and 80 °C [5]. In relative terms, coercivity falls about five times faster than strength as the magnet warms up. The practical check is the demagnetization curve at your operating temperature, for your magnet's dimensions. One manufacturer shows N42 and N42SH side by side at a reverse field of 15 kOe: N42 is pushed into the non-linear part of its curve, while N42SH stays linear and returns to its original Br once the field is removed [2].
A higher number is not always the better buy
One supplier puts N52 at about 20% more powerful than N42, at up to twice the price, and notes that two N42 magnets can be more useful than one N52 where space allows [4]. Some tables also give N52 a lower working temperature than N42 [1], [3]. So choose the number from the force you need and the space you have, and choose the letters from the temperature and from any opposing fields, such as those in motors or next to other magnets. Our articles on grades for high-temperature motors and where dysprosium and terbium matter cover the higher classes in more detail.
What to put in your enquiry
Write the full grade, for example N42SH, not just N42. Add the operating temperature range and the peak temperature, the dimensions, how the magnet sits in the assembly, and any opposing fields. If you do not know the grade, describe the temperature and the job and we will propose one. The rest of the checklist is in our RFQ guide, and the temperature selector maps your range to a material.
References
[1] Stanford Magnets. Neodymium magnets grade info. https://www.stanfordmagnets.com/neodymium-magnets-grade-info.html (accessed 21 October 2026)
[2] Advanced Magnets. How to understand the rare earth permanent magnets grades, part 1: sintered neodymium iron boron magnets. https://www.advancedmagnets.com/how-to-understand-the-rare-earth-permanent-magnets-grades-part-1-sintered-neodymium-iron-boron-magnets (accessed 21 October 2026)
[3] Eclipse Magnetics. Neodymium grades data (datasheet, PDF). https://www.eclipsemagnetics.com/site/assets/files/2399/neodymium_grades_data.pdf (accessed 21 October 2026)
[4] First4Magnets. Grades of neodymium magnets. https://www.first4magnets.com/neodymium-magnet-information/grades-of-neodymium-magnets (accessed 21 October 2026)
[5] Arnold Magnetic Technologies. Arnold Neo catalog (PDF). https://www.arnoldmagnetics.com/wp-content/uploads/2019/06/Arnold-Neo-Catalog.pdf (accessed 21 October 2026) [Supplier technical pages and datasheets, not the IEC standard; values vary by supplier.]