How to Select the Right Neodymium Magnet: A Procurement Guide

Neodymium magnets provide extremely high magnetic strength relative to their size, but selecting the right magnet requires more than choosing the highest available grade.

Procurement professionals must evaluate operating temperature, coercivity, dimensions, tolerances, magnetization direction, coating, environmental exposure, mechanical requirements, compliance documentation, and supplier quality controls. A magnet that appears acceptable on a product listing can fail when installed in an actual assembly if any of these factors are overlooked.

This guide explains how to specify and purchase neodymium magnets for industrial and commercial applications.

What Is a Neodymium Magnet?

A neodymium magnet is a permanent magnet manufactured primarily from neodymium, iron, and boron. The material is commonly identified as NdFeB or rare-earth–iron–boron.

Most industrial neodymium magnets are produced through a sintering process. Sintered NdFeB magnets combine high residual induction, coercivity, and maximum energy product, allowing engineers to generate substantial magnetic performance from a relatively small component.

IEC 60404-8-1 classifies sintered rare-earth–iron–boron magnets as Class R7 permanent-magnet materials. The standard identifies four principal properties used to characterize permanent magnets:

Maximum energy product, or (BH)max
Remanent flux density, or Br
Coercivity relating to flux density, or HcB
Intrinsic coercivity, or HcJ

These properties should appear on the material specification or supplier data sheet when magnetic performance is critical.

The Short Answer: How Do You Choose a Neodymium Magnet?

To select a neodymium magnet, define these eight requirements:

Required magnetic performance
Maximum operating temperature
Magnet shape and finished dimensions
Magnetization direction
Working air gap and mating steel
Environmental and corrosion exposure
Mechanical loads and assembly method
Quality, traceability, and regulatory requirements

Do not select a magnet grade based only on its N-number. The complete application determines whether the magnet will perform reliably.

Step 1: Understand Neodymium Magnet Grades

Commercial sintered neodymium grades are commonly identified by designations such as N35, N42, N48, or N52. A suffix may be added to identify a higher-coercivity material, producing designations such as N35SH, N42UH, or N38EH.

The number is associated with the material’s maximum energy product, generally expressed in megagauss-oersteds, or MGOe. For example, an N42 material normally has a maximum energy-product range centered near 42 MGOe.

A higher grade can provide greater magnetic output when magnet dimensions and magnetic-circuit conditions remain the same. However, the highest grade is not automatically the best choice.

Higher-energy grades may have:

Lower resistance to demagnetization at elevated temperatures
Higher material costs
More limited availability in certain shapes or sizes
Longer production lead times
Different heavy rare-earth content or manufacturing requirements

The objective is to select the lowest-cost grade that satisfies the magnetic and thermal requirements with an appropriate safety margin.

What Do the Grade Suffixes Mean?

Suffixes such as M, H, SH, UH, EH, and AH generally identify progressively higher intrinsic coercivity. Intrinsic coercivity measures a magnet’s resistance to irreversible demagnetization.

These suffixes should not be treated as universal temperature guarantees. Maximum operating temperature depends on the exact material formulation, magnet geometry, permeance coefficient, magnetic circuit, external demagnetizing fields, and the supplier’s qualification criteria.

For example, commercial product data show that temperature classifications can vary even among materials carrying familiar suffixes. TDK identifies one 42SH material with a 120°C temperature classification, while other specialized neodymium formulations are classified for 160°C or 180°C service. This is why procurement specifications should reference an approved material data sheet rather than relying on a generic suffix chart.

Procurement rule: Never write “N42SH or equivalent” without also specifying minimum Br, HcB, HcJ, (BH)max, operating temperature, and test conditions.

Step 2: Specify the Actual Operating Temperature

The maximum temperature surrounding the product is not always the magnet’s actual operating temperature.

The magnet may be heated by:

Motor windings
Friction
Nearby electronics
Solar exposure
Sterilization or cleaning processes
Restricted airflow
Thermal cycling
Heat conducted through the assembly

Neodymium magnets also experience a reversible reduction in magnetic output as temperature increases. Arnold Magnetic Technologies reports a reversible temperature coefficient of induction for neodymium materials of approximately −0.07% to −0.13% per degree Celsius, depending on the grade.

A magnet can therefore become temporarily weaker at an elevated temperature even when it does not suffer permanent damage. If the temperature or opposing magnetic field exceeds the material’s limits, irreversible demagnetization may occur.

A proper request for quotation should state:

Normal operating temperature
Maximum continuous temperature
Maximum short-duration temperature
Length and frequency of temperature exposure
Lowest operating temperature
Expected thermal cycles
External demagnetizing fields, if applicable

For critical applications, request a demagnetization curve for the proposed grade at the actual operating temperature.

Step 3: Define the Shape and Dimensions

Neodymium magnets are commonly supplied as:

Discs
Cylinders
Rings
Blocks
Arcs or segments
Countersunk magnets
Custom-machined shapes
Magnet-and-steel assemblies

Shape affects manufacturability, cost, magnetic performance, handling, and tooling requirements.

A complete dimensional specification should include:

Finished dimensions
Units of measurement
Dimensional tolerances
Edge condition
Chamfers or radii
Plating or coating thickness
Flatness, parallelism, or concentricity when required
Whether dimensions apply before or after coating

Avoid excessive tolerances. Sintered neodymium is hard and brittle, so tight tolerances generally require additional grinding and inspection. This increases cost without necessarily improving the performance of the final assembly.

If a dimension is not functionally critical, allow the supplier to recommend a practical production tolerance.

Step 4: State the Magnetization Direction

Magnetization direction is one of the most frequently omitted purchasing requirements.

Common configurations include:

Axial magnetization
Diametric magnetization
Magnetization through thickness
Magnetization through width
Radial magnetization
Multipole magnetization
Custom pole patterns

For a disc or ring, axial magnetization normally places the north and south poles on the two flat faces. Diametric magnetization places the poles on opposite sides of the circumference.

These configurations are not interchangeable.

The drawing should show the magnetization direction with an arrow or pole designation. If the assembly requires a specific north-pole orientation, inspection method, multipole pattern, or indexing feature, include it explicitly.

Step 5: Evaluate the Complete Magnetic Circuit

A magnet does not operate independently of its surroundings. Its performance is affected by:

Magnet dimensions
Air gap
Mating-steel thickness
Steel grade and saturation
Pole-piece geometry
Nearby magnets
Operating temperature
Direction of applied load
Surface condition
Assembly tolerances

This is why surface gauss and pull force should not be used interchangeably.

Surface Gauss vs. Pull Force

Surface gauss measures magnetic flux density at a defined point near the magnet’s surface.

Pull force measures the force required to separate the magnet from a specified ferromagnetic target under defined test conditions.

Pull-force results can change significantly with:

Steel thickness and composition
Surface roughness
Coating thickness
Air gap
Magnet orientation
Contact area
Pulling angle
Test speed

A pull-force value is meaningful only when the test setup is stated.

When comparing suppliers, require them to use the same fixture, steel target, gap, orientation, and acceptance method. Otherwise, two pull-force numbers may not represent equivalent performance.

Step 6: Select the Correct Coating

Sintered neodymium magnets are susceptible to corrosion and normally require a protective surface finish. Arnold Magnetic Technologies specifically identifies corrosion as a potential cause of energy loss or magnet failure in NdFeB materials.

Common finishes include:

Finish	Typical advantages	Important considerations
Nickel-copper-nickel	Common, economical and abrasion resistant	Can chip; verify suitability for humidity and chemical exposure
Epoxy	Improved barrier protection in many environments	Can scratch or wear during assembly
Zinc	Economical and suitable for selected general applications	Appearance and corrosion resistance vary by process
Phosphate	Thin and useful as a treatment or bonding surface	Limited protection unless combined with another system
Parylene	Thin, conformal and useful for specialized applications	Higher cost and process-specific limitations
Gold over nickel	Conductive and suitable for certain specialty uses	Expensive; underlying layers remain important
Uncoated	Appropriate only in controlled or specially engineered conditions	High corrosion risk in ordinary humid environments

Coating selection should consider humidity, salt exposure, chemicals, cleaning agents, handling, abrasion, electrical conductivity, biocompatibility, adhesive compatibility, and expected product life.

Do not request “nickel plating” alone when corrosion performance is important. Specify the complete coating system, thickness range, adhesion requirements, appearance criteria, and applicable environmental test.

Step 7: Account for Mechanical Properties

Neodymium magnets are strong magnetically but brittle mechanically. They can chip, crack, or fracture when struck, pressed into an undersized cavity, subjected to uneven clamping, or allowed to snap together.

They should generally not be treated like conventional load-bearing steel components.

Good assembly practices include:

Using a controlled clearance rather than an aggressive interference fit
Preventing magnets from snapping together
Distributing clamping loads evenly
Avoiding direct impact
Using adhesives compatible with the coating
Providing mechanical retention when bond failure would create a safety risk
Designing packaging that prevents magnet-to-magnet collisions

If a magnet will experience shock, vibration, rotation, repeated impact, or centrifugal force, specify those conditions during sourcing.

Step 8: Define the Required Quality Documentation

The required documentation should be established before the purchase order is released.

Depending on the application, procurement teams may request:

Certificate of Conformance
Material certification
Magnetic-property test report
Dimensional inspection report
Coating certification
Plating-thickness report
Magnetization verification
Pole-orientation inspection
Pull-force or surface-flux test report
Lot traceability
RoHS declaration
REACH and SVHC declaration
Conflict-minerals reporting
PFAS declaration
California Proposition 65 status
Country-of-origin documentation
Production Part Approval Process documentation

A supplier cannot reliably reconstruct every traceability record after a product has shipped. Documentation requirements should therefore be included on the RFQ and purchase order.

Neodymium Magnet RFQ Checklist

A procurement-ready request for quotation should contain the following information:

Requirement	Information to provide
Material	Sintered or bonded NdFeB
Grade	Requested grade plus minimum magnetic properties
Shape	Disc, ring, block, arc, cylinder or custom
Dimensions	Complete finished dimensions and units
Tolerances	Functional tolerances only
Magnetization	Direction, pole orientation and number of poles
Coating	Finish, thickness and performance requirement
Temperature	Normal, maximum, minimum and exposure duration
Magnetic requirement	Br, HcB, HcJ, (BH)max, flux, gauss or pull force
Test conditions	Fixture, air gap, target steel, temperature and equipment
Environment	Humidity, salt, chemicals, vacuum or sterilization
Mechanical exposure	Shock, vibration, rotation or clamping
Quantity	Prototype, annual demand and order frequency
Packaging	Individual separation, trays, spacers or shielding
Compliance	Required regulatory declarations
Quality records	Inspection report, COC, traceability or PPAP
Drawing control	Drawing number, revision and approval requirements

Common Procurement Mistakes

Selecting Only by Pull Force

A published pull-force value does not describe the complete test arrangement. Use it for initial screening, not as the sole acceptance criterion.

Assuming N52 Is Always Best

N52 offers high room-temperature energy density, but a lower-energy, higher-coercivity grade may provide better reliability in a hot or demagnetizing environment.

Using Maximum Operating Temperature as a Fixed Material Constant

Temperature capability depends on the grade, shape, magnetic circuit, external field, and supplier criteria. Review the proposed material’s demagnetization curves.

Omitting Magnetization Direction

Correct dimensions with the wrong magnetization direction can make the entire shipment unusable.

Ignoring the Air Gap

Paint, adhesive, plating, plastic, labels, surface curvature, and assembly clearance can all create an air gap that reduces holding force.

Specifying Unnecessarily Tight Tolerances

Overly restrictive tolerances increase grinding, inspection, scrap, cost, and lead time.

Requesting Compliance Documents After Shipment

Compliance and traceability requirements should be part of the original quotation and purchase order.

Approving a Sample Without Freezing the Specification

A successful sample should be connected to an approved drawing, grade, coating, magnetization requirement, and inspection plan before production begins.

How Should Procurement Teams Compare Magnet Suppliers?

Price per piece should be only one part of the evaluation.

A qualified supplier should be able to demonstrate:

Experience with the requested grade and application
Controlled sub-supplier or manufacturing sources
Material and lot traceability
Calibrated inspection equipment
Defined dimensional and magnetic test methods
Coating-quality controls
Consistent magnetization processes
Protective packaging procedures
Change-notification controls
Regulatory-document support
Corrective-action capability
Capacity for projected annual demand

The best supplier is not necessarily the company quoting the strongest grade or lowest unit price. It is the supplier that can consistently deliver the specified magnetic, dimensional, environmental, and documentation requirements.

Frequently Asked Questions

What is the strongest commercially available neodymium magnet grade?

N52 is commonly treated as one of the highest widely available standard commercial grades by maximum energy product. However, specialized materials and supplier-specific grades may offer different combinations of energy density, coercivity, and temperature capability. The strongest grade at room temperature is not always the best grade for the application.

What is the difference between N35 and N52?

N52 typically has a higher maximum energy product and can produce greater magnetic output than N35 in the same geometry and magnetic circuit. N35 may be more economical and can be fully adequate when the application does not require the additional energy density.

Does a larger grade number mean a higher operating temperature?

No. The grade number primarily relates to maximum energy product. Temperature resistance is more closely associated with intrinsic coercivity, the exact material formulation, magnet geometry, and magnetic circuit.

Can neodymium magnets rust?

Yes. Sintered NdFeB is vulnerable to corrosion and is normally protected by nickel, epoxy, zinc, Parylene, or another coating system selected for the operating environment.

Can neodymium magnets be machined after magnetization?

Machining a finished magnet is generally not recommended. Neodymium magnets are brittle, and machining can damage the coating, create hazardous dust, generate heat, and alter performance. Dimensions and features should normally be completed by the manufacturer before final coating and magnetization.

How should neodymium magnets be stored?

Store magnets in a clean, dry, temperature-controlled environment. Keep them separated to prevent impact damage, protect their coatings, and maintain appropriate distance from sensitive electronics, magnetic media, medical devices, and unprotected personnel.

What information is needed to quote a custom neodymium magnet?

At minimum, provide the grade, dimensions, tolerances, coating, magnetization direction, quantity, operating temperature, application environment, magnetic-performance requirement, drawing revision, and required quality documentation.

Final Recommendation

A reliable neodymium magnet specification connects material properties to the actual application.

Procurement professionals should avoid selecting magnets solely by grade number, surface gauss, pull force, or unit price. The better approach is to define the complete operating environment, establish measurable acceptance criteria, and require documentation appropriate to the product’s risk.

Radial Magnets helps procurement teams and manufacturers source standard and custom neodymium magnets with clearly defined grades, dimensions, coatings, magnetization patterns, inspection requirements, and compliance documentation.

For assistance evaluating an existing magnet specification or preparing an RFQ, contact Radial Magnets before releasing the production order.