Every NdFeB quotation carries a grade like N42 or N48SH. That short code contains two independent decisions — one about magnetic strength, one about temperature survival — and confusing the two is the single most common grade-selection error we see.
The Number: Maximum Energy Product
The number after "N" is the magnet's maximum energy product, (BH)max, in Mega-Gauss-Oersteds (MGOe). It tells you how much magnetic energy a given volume of material can deliver. N35 stores roughly 35 MGOe; N52 roughly 50–53 MGOe — the practical ceiling of commercial production.
In design terms: a higher number means the same flux from a smaller magnet, or more flux from the same volume. It says nothing about temperature resistance.
| Grade | Remanence Br (typical) | (BH)max (typical) | Design note |
|---|---|---|---|
| N35 | 1.17–1.21 T | 33–36 MGOe | Workhorse grade, best cost efficiency |
| N42 | 1.29–1.33 T | 40–43 MGOe | Common default for motors |
| N48 | 1.37–1.41 T | 46–49 MGOe | Compact designs |
| N52 | 1.42–1.47 T | 50–53 MGOe | Highest commercial strength; tightest geometry tolerance needed |
Typical ranges — exact values vary slightly between manufacturers and material lots.
The Letter: Coercivity and Temperature Survival
The letter suffix (M, H, SH, UH, EH) indicates intrinsic coercivity Hcj — the material's resistance to demagnetization — which in practice defines its maximum operating temperature. Higher coercivity is achieved with heavy rare earth content (dysprosium or terbium), which is why high-temperature grades cost significantly more.
| Suffix | Intrinsic coercivity Hcj (min., typical) | Max. operating temperature |
|---|---|---|
| (none) | ≥ 12 kOe | ≈ 80°C |
| M | ≥ 14 kOe | ≈ 100°C |
| H | ≥ 17 kOe | ≈ 120°C |
| SH | ≥ 20 kOe | ≈ 150°C |
| UH | ≥ 25 kOe | ≈ 180°C |
| EH | ≥ 30 kOe | ≈ 200°C |
AH grades (≈ 220–230°C) exist for special cases. Above that, you are in SmCo territory — see our material comparison.
Why the Temperature Rating Matters More Than Strength
NdFeB loses flux two ways when hot. Reversible loss (about −0.12 %/°C for Br) comes back when the magnet cools. Irreversible loss does not: once the operating point crosses the material's knee point, the magnet is permanently weaker — and your motor, sensor or latch now underperforms forever, even though nothing looks damaged.
The classic failure: an engineer specifies N52 for maximum performance in a motor that runs at 110–120°C. N52 has no temperature suffix — it is an 80°C-class material. The samples test beautifully at room temperature; six months into field operation, the irreversible losses show up as torque fade and customer complaints.
Rule of thumb: the strongest magnet is the one that is still magnetized at your operating temperature. An N42SH that survives will outperform an N52 that doesn't.
A Four-Step Selection Workflow
- Define your true maximum operating temperature — including worst-case ambient, self-heating, and transient peaks. Add margin.
- Choose the suffix first. Temperature survival is non-negotiable; flux can be recovered with geometry.
- Choose the lowest N-number that meets your flux requirement. Every step up in strength or coercivity adds cost; high-coercivity grades carry heavy-rare-earth premiums.
- Validate at temperature, not at the desk. Sample testing should include your real thermal profile, not just room-temperature flux checks.
What We Ask Before Quoting a Grade
When you send us an inquiry, expect these questions: continuous and peak operating temperature, external demagnetizing fields (in motors and sensors), required flux or holding force, and available volume. With those four answers, grade selection stops being guesswork — and you don't pay for dysprosium you don't need.