Sintered NdFeB magnets are graded by their maximum energy product (BHmax), measured in megagauss-oersteds (MGOe). The number in the grade name — N35, N42, N52 — corresponds roughly to this value. A higher number means more magnetic energy per unit volume. But choosing the right grade involves more than picking the highest number.
Understanding the Grade Naming System
The "N" prefix indicates standard temperature rating (up to ~80°C continuous operating temperature). Suffixes modify the temperature performance: H (120°C), SH (150°C), UH (180°C), EH (200°C), and AH (220°C). So an N42SH magnet has a BHmax around 42 MGOe with a maximum operating temperature of 150°C. Higher temperature ratings require more dysprosium or terbium in the alloy, which increases cost.
Common Grades and Their Applications
N35–N38: Entry-level grades suitable for sensors, consumer electronics, and low-performance motors. Cost-effective when high flux density isn't critical. Often the right choice for prototyping or applications where size constraints are loose.
N42–N45: The workhorse range for industrial motors, actuators, and magnetic assemblies. These grades offer a strong balance of performance and cost. Most SME motor manufacturers should start their grade selection here.
N48–N52: Premium grades for applications where size and weight are tightly constrained — aerospace, medical devices, high-performance drones. The cost premium over N42 is significant (30–50%), and availability of non-Chinese material in these grades is more limited.
The Over-Specification Trap
One of the most common mistakes in magnet procurement is specifying a higher grade than the application requires. An engineer might request N52 when N42 would deliver identical system performance with a slightly larger magnet. The cost difference is substantial — not just in material price, but in lead time and sourcing flexibility. Non-Chinese N42 and N45 grades are widely available from Tier 1 suppliers. Non-Chinese N52 is significantly harder to source.
Temperature Rating Selection
Select your temperature suffix based on the actual operating environment of the magnet, not worst-case theoretical maximums. A motor that runs at 60°C continuous doesn't need SH-grade material — standard N-grade is sufficient with margin. Over-specifying temperature rating adds dysprosium cost without functional benefit.
Practical Recommendation
For most SME motor and actuator applications, start with N42 or N42H. These grades offer excellent performance, broad availability from non-Chinese sources, competitive pricing, and reasonable lead times. Only move to higher grades if your design analysis specifically requires it — and if it does, consider whether a geometry change could achieve the same result with a lower grade.