This guide explains the specifications you'll find on our product pages: grade, temperature class, coating, magnetisation direction and pull force. It'll help you compare products and choose the right magnet for your application. The values below are typical industry figures for each grade or class. The data on the product page (or the datasheet for the product) always takes precedence.
1. Neodymium magnet grades (N35–N52)
Neodymium magnets (NdFeB, an alloy of neodymium, iron and boron) are graded by the strength of the material. In a grade such as N42:
- N stands for neodymium.
- 42 is the maximum energy product, (BH)max, in MGOe (mega-gauss-oersteds). The higher the number, the more magnetic energy per unit of volume, so the stronger the magnet for the same size.
- A letter after the number (for example N42SH) shows a higher temperature class (see section 2). No letter means a standard grade.
Typical values for standard grades
| Grade | Remanence Br (T) | Max. energy product (BH)max (MGOe) | (BH)max (kJ/m³, approx.) |
|---|---|---|---|
| N35 | 1.17–1.22 | 33–36 | 263–286 |
| N38 | 1.22–1.26 | 36–39 | 286–310 |
| N40 | 1.26–1.29 | 38–41 | 302–326 |
| N42 | 1.29–1.32 | 40–43 | 318–342 |
| N45 | 1.32–1.38 | 43–46 | 342–366 |
| N48 | 1.38–1.42 | 45–49 | 358–390 |
| N50 | 1.40–1.45 | 47–51 | 374–406 |
| N52 | 1.43–1.48 | 49–53 | 390–422 |
Typical ranges as published in common industry grade tables; exact values vary slightly between manufacturers.
What this means in practice
- A higher grade gives more holding force from the same size, or the same force from a smaller magnet. That's useful when space is limited.
- Size usually has a bigger effect on pull force than grade: a slightly larger magnet in a lower grade can be as strong as a smaller one in a higher grade.
- Higher grades cost more and aren't more heat resistant. Standard high grades such as N50 and N52 are no better at high temperatures than N35.
- All neodymium grades are equally brittle and need the same care in handling.
2. Temperature classes and maximum operating temperature
Neodymium magnets lose strength as they get warmer. Up to the maximum operating temperature, this loss is largely reversible: the magnet recovers when it cools down. Above that temperature, part of the strength is lost permanently. At the Curie temperature (roughly 310–340 °C for standard NdFeB) the magnet loses its magnetisation completely.
The letter after the grade number shows the temperature class. Grades with a higher class have a higher coercivity (resistance to demagnetisation).
| Suffix | Example | Typical max. operating temperature | Min. intrinsic coercivity Hcj |
|---|---|---|---|
| (none) | N35–N52 | 80 °C | ≥ 12 kOe (955 kA/m) |
| M | N45M | 100 °C | ≥ 14 kOe (1,114 kA/m) |
| H | N42H | 120 °C | ≥ 17 kOe (1,353 kA/m) |
| SH | N42SH | 150 °C | ≥ 20 kOe (1,592 kA/m) |
| UH | N35UH | 180 °C | ≥ 25 kOe (1,990 kA/m) |
| EH | N35EH | 200 °C | ≥ 30 kOe (2,388 kA/m) |
| AH | N33AH | 220–230 °C | ≥ 35 kOe (2,785 kA/m) |
Widely published standard values, as a guide only. Please note:
- The maximum operating temperature in practice depends on the shape of the magnet and the application. Thin, flat magnets (for example thin discs) demagnetise at lower temperatures than the table suggests, as do magnets exposed to opposing magnetic fields.
- Some manufacturers specify a lower maximum temperature for the highest standard grades (N50–N52). Where we have the value, the product page shows the maximum operating temperature for that product.
- Coatings and housings can set a lower limit than the magnet: rubber, plastic and self-adhesive layers may not withstand the magnet's full temperature rating.
- Where we have the maximum operating temperature for a product, it's shown on the product page.
Other magnet materials in our range
- Ferrite (ceramic) magnets: weaker than neodymium, but corrosion-resistant and usable at higher temperatures (generally up to about 250 °C). Ferrite can lose strength at very low temperatures.
- Alnico magnets: suitable for high temperatures (generally several hundred °C), but relatively easy to demagnetise.
- Flexible magnetic tape and sheet: magnetic powder in a flexible binder, for light holding over larger areas. The binder and any adhesive layer limit the temperature; check the product page.
3. Coatings
Neodymium corrodes quickly if left unprotected, so neodymium magnets always have a protective coating or housing. The right coating depends on where the magnet will be used.
| Coating | Appearance | Properties | Typical use |
|---|---|---|---|
| Nickel (Ni-Cu-Ni) | Shiny silver | The most common coating: three layers (nickel, copper, nickel). Hard, smooth surface with good protection in dry conditions. Can trigger reactions in people with a nickel allergy on prolonged skin contact. | Indoor use in dry environments; general purpose |
| Zinc (Zn) | Matt bluish-grey or silver | Lower-cost coating; generally offers less corrosion and wear resistance than nickel. | Dry indoor use; parts that are glued in place |
| Epoxy | Usually black or grey | Better protection against humidity than metal coatings; softer, so it scratches more easily. Often combined with a nickel or copper under-layer. | Humid indoor environments; applications where a non-metallic surface is preferred |
| Rubber | Usually black (other colours possible) | Thick, protective layer that prevents scratches and increases friction, so the magnet resists sliding better. Protects the magnet against moisture and knocks. The layer acts as a small air gap, so pull force is lower than for an uncoated magnet of the same size. | Painted or delicate surfaces, vehicles, outdoor and temporary mounting |
Our range also includes plastic-coated magnets and stainless-steel housings (for example filter magnets and some pot magnets). Check the product page for the coating or housing of each product.
Tips
- A damaged coating exposes the neodymium to moisture and it will start to corrode. Avoid magnets snapping together, which chips the coating.
- No standard coating makes a neodymium magnet suitable for permanent use in water or salty environments unless the product description says so.
- For outdoor use, choose a rubber-coated or housed magnet, or protect the magnet yourself (for example by sealing it in).
4. Magnetisation direction
The magnetisation direction describes where the north and south poles are. It matters when magnets need to attract or repel each other, or work with sensors.
- Axial (through the thickness or length): the poles are on the two flat faces. Discs, rods and rings are normally axially magnetised through their height or thickness unless stated otherwise.
- Diametrical: the poles are on the curved sides, across the diameter. Used for rotary sensors, couplings and some holding applications. Diametrically magnetised products say so in their title.
- Block magnets: In block magnet titles (for example, 20 x 10 x 5 mm), the last dimension is the magnetisation direction: the magnet is magnetised through its thickness.
- Pot magnets (mounting magnets): the steel housing concentrates the magnetic field on the open face, so both poles are on one side and the holding force is concentrated there. The back and sides are hardly magnetic.
- Magnetic tape and sheet: usually magnetised with many narrow alternating poles on one side. Two pieces of tape only hold well together when they are matched to each other.
- North or south face: some products are sold with a specified pole on the front face. To make two such magnets attract face to face, combine a north-face version with a south-face version.
5. Pull force: what the figures mean
How it's measured. The pull force (also called holding force or adhesive force) we list is an indicative value in kilograms: the force needed to pull the magnet straight off a flat, polished steel plate that's thick enough not to limit the result, with the full surface in contact, at room temperature. These figures come from our suppliers' data.
They are laboratory values measured under ideal conditions. In real applications, the holding force is lower, often considerably.
What reduces pull force
- Air gap: any distance between magnet and steel reduces the force sharply. Paint, powder coating, rust, dirt, tape, labels, a sheet of paper or a rubber coating all act as an air gap. Even a gap of a fraction of a millimetre can make a noticeable difference, especially for small magnets and pot magnets.
- Steel thickness: thin steel sheet can't absorb the full magnetic field. On thin sheet metal, a strong magnet holds much less than on a thick plate.
- Type of steel: low-carbon (mild) steel gives the best result. Cast iron and alloyed or hardened steels give less holding force. Most stainless steels (such as the common grades 304 and 316) are barely magnetic or not magnetic at all. Aluminium, copper, brass, wood, glass and plastic aren't magnetic.
- Surface and contact area: a rough, curved or uneven surface, or partial contact (for example at an edge), reduces the force.
- Direction of load (shear): the listed force applies to a straight, perpendicular pull. When a load pulls parallel to the surface (for example a magnet on a vertical steel wall carrying a weight), the magnet slides off at a much lower force. Rubber-coated magnets resist sliding better.
- Temperature: the warmer the magnet, the weaker it is (see section 2).
- Dynamic loads: vibration, shocks and repeated loading can make a magnet let go well below its rated force.
- Magnet to magnet: the force between two magnets differs from the force between a magnet and steel, and depends on both magnets.
Choosing the right magnet
- Test the magnet in your actual application and allow a generous safety margin.
- Don't use magnets on their own to hold loads above people, or in any application where failure could cause injury or damage, unless the design has been checked and tested by a qualified person.
- Not sure which size you need? Send us your application details and we'll help you choose: info@magneticsolutions.net.
6. Dimensions and tolerances
Dimensions are given in millimetres. Discs: diameter x thickness (for example 10 x 3 mm). Rods: diameter x length. Blocks: length x width x height. Rings: outer diameter x inner diameter x height (check the product title for the order used). Typical dimensional tolerance is ±0.1 to 0.2 mm, depending on size and product type. The tolerance for each product is stated per product where known and can be confirmed on request via info@magneticsolutions.net or the quote form.
7. Glossary
- Remanence (Br): the magnetic flux density remaining in the material after magnetisation, in tesla (T) or kilogauss (kG). 1 T = 10 kG.
- Coercivity (Hcb, Hcj): the material's resistance to demagnetisation. The intrinsic coercivity Hcj determines how well a magnet withstands heat and opposing fields.
- Maximum energy product ((BH)max): a measure of the magnetic energy stored in the material, in MGOe or kJ/m³. Its value gives the grade number.
- Surface field strength (gauss or mT): the field measured at the surface of the magnet, as stated for our filter magnets, for example. 1 mT = 10 gauss. It isn't the same as pull force.
- Maximum operating temperature: the highest temperature at which the magnet can be used without significant permanent loss of strength (under typical conditions).
- Curie temperature: the temperature at which a material loses its magnetism completely.
Questions about a specification? Email us at info@magneticsolutions.net.