You specified N42, then the thermal simulation came back hotter than you hoped — or a field unit lost torque after a few hundred hours. That is the moment most engineers reach the N42 vs N42SH question. Both grades carry the same ~42 MGOe of strength on the bench. The difference is whether that strength survives the temperature your part actually reaches in service.
What do the N42 and N42SH grades actually mean?
The number in any neodymium magnet grade[3] reports how much magnetic energy the material can store. N42 and N42SH both sit at 42 MGOe, so on a room-temperature pull test they read almost the same. The suffix is the whole story here.
The letter code is a temperature ladder tied to intrinsic coercivity: no letter is standard (80°C), then M (100°C), H (120°C), SH (150°C), UH (180°C), EH (200°C). "SH" means super-high coercivity. Buying that extra heat tolerance means adding heavy rare earth — typically 1–4.5% dysprosium — which lifts Hcj without raising BHmax.
| Property | N42 | N42SH |
|---|---|---|
| Max energy product (BHmax) | 40–43 MGOe | 40–43 MGOe |
| Remanence (Br) | ~1.28–1.32 T | ~1.28–1.32 T |
| Max operating temperature | 80°C | 150°C |
| Intrinsic coercivity (Hcj) | ≥12 kOe | ≥20 kOe |
| Added dysprosium | Minimal | ~1–4.5% |
| Temp coefficient of Br | ~−0.11%/°C | ~−0.11%/°C |
| Relative price | Baseline | +10–15% |
Same strength, very different thermal envelope. The real engineering question is whether your part reaches the temperature that justifies paying for SH — and that depends on more than the ambient number on your datasheet.
What happens to N42 above 80°C — and why "ambient" is the wrong number
Watch the knee point move with temperature
Second-quadrant B–H demagnetization curve. Raise the temperature and watch where each grade crosses into irreversible loss.
Simplified illustration — trends only, not absolute datasheet values.
Two things trip up engineers on this comparison. First, the temperature rating is a guide value, not a hard wall — the true limit is set by the whole magnetic circuit. A thin magnet, or one with a low permeance coefficient, can begin to demagnetize below its nominal rating. A thick magnet backed by steel can sometimes run slightly past it. That is why a thin N42 in a hot motor fails while a chunky N42 block at the same air temperature survives.
Second, the magnet runs far hotter than the room. Inside a sealed motor, an EV drive unit, or any continuous-duty assembly, internal temperature climbs well above ambient. A passively cooled motor housing routinely sits at 110–130°C in normal duty — comfortably past the point where N42 quietly fails and exactly where N42SH earns its premium.
Working rule our engineers use: take the highest temperature the magnet will ever reach (cross-reference your thermal simulation, not just the ambient spec), add 20–30°C of margin, then pick the grade rated above that number. For continuous-duty motors, that almost always pushes an "80°C application" up to an SH grade.
Continuous duty vs short bursts: the duty-cycle test
This is the practical line that decides most of these cases. A cordless-tool motor that runs in two-minute bursts with airflow between cycles behaves very differently from a chemical-pump motor that runs for hours in a sealed housing. Same nominal load, completely different magnet temperature. Map your duty cycle before you map your grade.
If you are specifying for motion, our application pages go deeper on grade and rotor geometry for EV motors, robotics, and industrial motors, and our DC motor magnets page covers arc segments and radial multipole rings for rotors.
Dysprosium is the lever that raises coercivity, and it is one of the heavy rare earths now under export licensing[4]. Two consequences for your spec: SH-class magnets cost more per kilo, and their lead time can be more sensitive to rare earth supply than a plain N42. Specifying SH where the part never gets hot means paying a heavy-rare-earth premium for headroom you never use.
The flip side is the cost of under-specifying. A demagnetized magnet in a fielded motor is never a cheap fix — it means a returned unit, a teardown, and usually a redesign. Against that, a 10–15% material premium is cheap insurance. The expensive mistake is almost always the one that ships.
Which applications suit N42 vs N42SH?
| Application | Typical magnet temp | Recommended |
|---|---|---|
| Holding, fixtures, signage | <60°C | N42 |
| Sensors / encoders (cool zone) | <80°C | N42 |
| Consumer electronics, intermittent duty | <70°C | N42 |
| BLDC / servo motors (continuous) | 100–150°C | N42SH |
| Under-hood automotive sensors / actuators | 105–150°C | N42SH |
| Magnetic couplings, sealed pumps | 100–140°C | N42SH |
When you send the inquiry, have these ready
• Peak magnet temperature (from thermal sim or measurement), and duty cycle (continuous vs burst)
• Magnet geometry — especially thickness, since thin parts erode the effective temperature limit
• Magnetic circuit context (backing steel? opposing field? field-weakening?)
• Coating environment (humidity, salt-fog, adhesive bonding) and target tolerance
Not sure if your motor needs SH?
Send your peak temperature, duty cycle, and magnet geometry. We will tell you the lowest grade that is safe in service — then quote it.
Get a grade recommendationHow to choose for your procurement spec
The decision in one line
Map the magnet's hottest real working temperature, add margin, then pick the grade rated above it. Do not over-specify SH where N42 is safe; never save 12% on N42 where the part runs hot.
Working temp stays under 80°C, the duty is intermittent or ventilated, cost matters, and the part is not sealed or motor-driven. The standard workhorse for most general magnet jobs.
Continuous motor duty, sealed housings, under-hood heat, or a thin geometry that erodes the effective limit. Reliability over a small heavy-rare-earth premium.
One procurement warning: the grade stamp alone guarantees nothing. A magnet labelled N42SH from a loose supplier can carry too little dysprosium to actually hold 150°C, or test closer to N40 on strength. Ask for the demagnetization curve at temperature and the measured Hcj on your actual part — not a generic datasheet. For motor and automotive volumes, ask whether the supplier runs 100% inspection rather than sampling; with 1–2 kg of NdFeB in a typical drive motor, batch-to-batch consistency is what keeps your assembly line running. Mainrich holds a 99% consistency rate across mass production and tests temperature ratings on real parts.
