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MP 40x20x5 / N38 - ring magnet

ring magnet

Catalog no 030199

GTIN/EAN: 5906301812166

5.00
Load capacity 7.24 kg / 70.98 N Magnetic Induction 150.36 mT / 1504 Gs
Diameter
40 mm [±0,1 mm]
internal diameter Ø
20 mm [±0,1 mm]
Height
5 mm [±0,1 mm]
Weight
35.34 g
Magnetization Direction
↑ axial
Coating
[NiCuNi] Nickel

How we measure these parameters — certificates and measurements

check technical specifications »

9.95 zł net / pcs

12.24 zł with VAT (23% VAT) / pcs

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Frequently asked questions

What is the hole in a ring magnet for?
For mounting on a screw or a shaft. The bore may be cylindrical or countersunk for a screw head. The hole removes magnet volume, so a ring holds less than a disc of the same outside diameter.
What is the polarisation?
Axial as standard — poles on the flat faces of the ring. Diametrical polarisation is made to order.
What sizes are available?
Outside diameter from 5 to 62 mm from stock. To order up to 200 mm outside diameter, 180 mm bore and 40 mm height, with a lead time of 25–35 days.

Guides from the knowledge base

Engineering report for this magnet

Full PDF analysis: pull and shear force, effect of distance, temperature and plate thickness, safety distances and the demagnetization curve.

PDF report Calculator
Want to talk magnets?

Call us now +48 888 99 98 98 alternatively let us know using contact form the contact section.
Specifications and structure of a neodymium magnet can be estimated using our power calculator.

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Technical of the product - MP 40x20x5 / N38 - ring magnet

Specification / characteristics - MP 40x20x5 / N38 - ring magnet

properties
properties values
Cat. no. 030199
GTIN/EAN 5906301812166
Production/Distribution Dhit sp. z o.o.
ul. Zielona 14 05-850 Ożarów Mazowiecki PL
Country of origin Poland / China / Germany
Customs code 85059029
Diameter 40 mm [±0,1 mm]
internal diameter Ø 20 mm [±0,1 mm]
Height 5 mm [±0,1 mm]
Weight 35.34 g
Magnetization Direction ↑ axial
Load capacity ~ ? 7.24 kg / 70.98 N
Magnetic Induction ~ ? 150.36 mT / 1504 Gs
Coating [NiCuNi] Nickel
Manufacturing Tolerance ±0.1 mm

Magnetic properties of material N38

Specification / characteristics MP 40x20x5 / N38 - ring magnet
properties values units
Remanence Br ? 12.2-12.6 kGs
Remanence Br ? 1220-1260 mT
Coercivity bHc ? 10.8-11.5 kOe
Coercivity bHc ? 860-915 kA/m
Intrinsic coercivity iHc ≥ 12 kOe
Intrinsic coercivity iHc ≥ 955 kA/m
Energy product BHmax ? 36-38 BH max MGOe
Energy product BHmax ? 287-303 BH max KJ/m
Maximum working temperature ? ≤ 80 °C

Physical properties of sintered neodymium magnets Nd2Fe14B at 20°C

Physical properties of sintered neodymium magnets Nd2Fe14B at 20°C
properties values units
Vickers hardness ≥550 Hv
Density ≥7.4 g/cm3
Curie Temperature TC 310 °C
Curie Temperature TF 590 °F
Specific resistance 150 μΩ⋅cm
Bending strength 250 MPa
Compressive strength 1000~1100 MPa
Thermal expansion parallel (∥) to orientation (M) (3-4) x 10-6 °C-1
Thermal expansion perpendicular (⊥) to orientation (M) -(1-3) x 10-6 °C-1
Young's modulus 1.7 x 104 kg/mm²

Technical modeling of the magnet - technical parameters

These information constitute the result of a engineering analysis. Results are based on algorithms for the class Nd2Fe14B. Operational conditions may deviate from the simulation results. Use these calculations as a preliminary roadmap when designing systems.

Table 1: Static pull force (pull vs distance) - characteristics
MP 40x20x5 / N38

Distance (mm) Induction (Gauss) / mT Pull Force (kg/lbs/g/N) Risk Status
0 mm 5269 Gs
526.9 mT
 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
 strong
1 mm 5005 Gs
500.5 mT
 6.53 kg / 14.41 LBS
6534.7 g / 64.1 N
 strong
2 mm 4739 Gs
473.9 mT
 5.86 kg / 12.91 LBS
5857.7 g / 57.5 N
 strong
3 mm 4475 Gs
447.5 mT
 5.22 kg / 11.51 LBS
5222.2 g / 51.2 N
 strong
5 mm 3960 Gs
396.0 mT
 4.09 kg / 9.02 LBS
4090.8 g / 40.1 N
 strong
10 mm 2832 Gs
283.2 mT
 2.09 kg / 4.61 LBS
2092.3 g / 20.5 N
 strong
15 mm 1990 Gs
199.0 mT
 1.03 kg / 2.28 LBS
1033.4 g / 10.1 N
 weak grip
20 mm 1407 Gs
140.7 mT
 0.52 kg / 1.14 LBS
516.3 g / 5.1 N
 weak grip
30 mm 745 Gs
74.5 mT
 0.14 kg / 0.32 LBS
144.6 g / 1.4 N
 weak grip
50 mm 268 Gs
26.8 mT
 0.02 kg / 0.04 LBS
18.7 g / 0.2 N
 weak grip
Magnetic force decreases drastically per each millimeter of gap. Note that every additional insulation layer (e.g., contamination, paint, veneer) significantly weakens the grip. Neodymiums hold most effectively at the point of direct contact; gap drastically cuts the force. Observe how rapidly the parameters drop, when the product does not adhere directly to the metal substrate. When planning the arrangement, avoid unnecessary gaps.

Table 2: Slippage capacity (vertical surface)
MP 40x20x5 / N38

Distance (mm) Friction coefficient Pull Force (kg/lbs/g/N)
0 mm Stal (~0.2) 1.45 kg / 3.19 LBS
1448.0 g / 14.2 N
1 mm Stal (~0.2) 1.31 kg / 2.88 LBS
1306.0 g / 12.8 N
2 mm Stal (~0.2) 1.17 kg / 2.58 LBS
1172.0 g / 11.5 N
3 mm Stal (~0.2) 1.04 kg / 2.30 LBS
1044.0 g / 10.2 N
5 mm Stal (~0.2) 0.82 kg / 1.80 LBS
818.0 g / 8.0 N
10 mm Stal (~0.2) 0.42 kg / 0.92 LBS
418.0 g / 4.1 N
15 mm Stal (~0.2) 0.21 kg / 0.45 LBS
206.0 g / 2.0 N
20 mm Stal (~0.2) 0.10 kg / 0.23 LBS
104.0 g / 1.0 N
30 mm Stal (~0.2) 0.03 kg / 0.06 LBS
28.0 g / 0.3 N
50 mm Stal (~0.2) 0.00 kg / 0.01 LBS
4.0 g / 0.0 N
This section defines the theoretical force required to initiate the downward movement of the magnet vertically against a vertical steel wall (considering typical friction coefficient). This value is relative to the gap size between the magnet and the metal.

Table 3: Wall mounting (sliding) - vertical pull
MP 40x20x5 / N38

Surface type Friction coefficient / % Mocy Max load (kg/lbs/g/N)
Raw steel
µ = 0.3 30% Nominalnej Siły
2.17 kg / 4.79 LBS
2172.0 g / 21.3 N
Painted steel (standard)
µ = 0.2 20% Nominalnej Siły
1.45 kg / 3.19 LBS
1448.0 g / 14.2 N
Oily/slippery steel
µ = 0.1 10% Nominalnej Siły
0.72 kg / 1.60 LBS
724.0 g / 7.1 N
Magnet with anti-slip rubber
µ = 0.5 50% Nominalnej Siły
3.62 kg / 7.98 LBS
3620.0 g / 35.5 N
When placing a element on a vertical wall (e.g., a fridge), it will only hold just approx. 1/5 of its maximum pull force. Gravity as well as a weak degree of grip influence the fact that holders move down easier than they pop off the substrate. Want to create a hanger? Note that the shear force is much weaker than the maximum static pull force. On a smooth steel, the element will slip down under a significantly smaller load. Using a rubber coating can drastically raise the stability.

Table 4: Material efficiency (saturation) - sheet metal selection
MP 40x20x5 / N38

Steel thickness (mm) % power Real pull force (kg/lbs/g/N)
0.5 mm
10%
 0.72 kg / 1.60 LBS
724.0 g / 7.1 N
1 mm
25%
 1.81 kg / 3.99 LBS
1810.0 g / 17.8 N
2 mm
50%
 3.62 kg / 7.98 LBS
3620.0 g / 35.5 N
3 mm
75%
 5.43 kg / 11.97 LBS
5430.0 g / 53.3 N
5 mm
100%
 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
10 mm
100%
 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
11 mm
100%
 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
12 mm
100%
 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
A thin metal plate cannot take in the full magnetic flux, which weakens actual performance of the holder. Should you attach a powerful product to a weak sheet, the field will penetrate right through and the attraction force will be weaker. To utilize 100% of this magnet's potential, you require a sufficiently solid backing of metal. The material oversaturation causes that on sheet metal structures (e.g., appliance housings), the magnet holds weaker. We recommend selecting the steel dimension based on the following data.

Table 5: Thermal stability (material behavior) - power drop
MP 40x20x5 / N38

Ambient temp. (°C) Power loss Remaining pull (kg/lbs/g/N) Status
20 °C 0.0% 7.24 kg / 15.96 LBS
7240.0 g / 71.0 N
 OK
40 °C -2.2% 7.08 kg / 15.61 LBS
7080.7 g / 69.5 N
 OK
60 °C -4.4% 6.92 kg / 15.26 LBS
6921.4 g / 67.9 N
 OK
80 °C -6.6% 6.76 kg / 14.91 LBS
6762.2 g / 66.3 N
100 °C -28.8% 5.15 kg / 11.36 LBS
5154.9 g / 50.6 N
Classic neodymiums irreversibly lose parameters after exceeding the maximum temperature. Protect against heat – excessive heat can irreversibly demagnetize this product. As the temperature rises, the magnet's capacity momentarily drops. Do not use this product near heat sources exceeding its safe range. Exceeding the critical threshold will cause destruction of magnetic properties.
*Important note: Temperature resistance is determined by both grade, but also on the magnet's shape. Low-profile magnets (low permeance coefficient) are more susceptible to demagnetization sooner than long magnets. Red status in the table points to a risk of irreversible loss for this specific geometry.

Table 6: Two magnets (repulsion) - forces in the system
MP 40x20x5 / N38

Gap (mm) Attraction (kg/lbs) (N-S) Sliding Force (kg/lbs/g/N) Repulsion (kg/lbs) (N-N)
0 mm 179.94 kg / 396.69 LBS
5 920 Gs
26.99 kg / 59.50 LBS
26991 g / 264.8 N
 N/A
1 mm 171.16 kg / 377.35 LBS
10 277 Gs
25.67 kg / 56.60 LBS
25675 g / 251.9 N
 154.05 kg / 339.62 LBS
~0 Gs
2 mm 162.41 kg / 358.05 LBS
10 011 Gs
24.36 kg / 53.71 LBS
24361 g / 239.0 N
 146.17 kg / 322.24 LBS
~0 Gs
3 mm 153.87 kg / 339.24 LBS
9 744 Gs
23.08 kg / 50.89 LBS
23081 g / 226.4 N
 138.49 kg / 305.31 LBS
~0 Gs
5 mm 137.55 kg / 303.25 LBS
9 213 Gs
20.63 kg / 45.49 LBS
20633 g / 202.4 N
 123.80 kg / 272.92 LBS
~0 Gs
10 mm 101.67 kg / 224.14 LBS
7 921 Gs
15.25 kg / 33.62 LBS
15251 g / 149.6 N
 91.50 kg / 201.73 LBS
~0 Gs
20 mm 52.00 kg / 114.64 LBS
5 665 Gs
7.80 kg / 17.20 LBS
7800 g / 76.5 N
 46.80 kg / 103.18 LBS
~0 Gs
50 mm 6.64 kg / 14.64 LBS
2 025 Gs
1.00 kg / 2.20 LBS
996 g / 9.8 N
 5.98 kg / 13.18 LBS
~0 Gs
60 mm 3.59 kg / 7.92 LBS
1 489 Gs
0.54 kg / 1.19 LBS
539 g / 5.3 N
 3.23 kg / 7.13 LBS
~0 Gs
70 mm 2.03 kg / 4.48 LBS
1 120 Gs
0.30 kg / 0.67 LBS
305 g / 3.0 N
 1.83 kg / 4.03 LBS
~0 Gs
80 mm 1.20 kg / 2.64 LBS
860 Gs
0.18 kg / 0.40 LBS
180 g / 1.8 N
 1.08 kg / 2.38 LBS
~0 Gs
90 mm 0.73 kg / 1.62 LBS
673 Gs
0.11 kg / 0.24 LBS
110 g / 1.1 N
 0.66 kg / 1.46 LBS
~0 Gs
100 mm 0.47 kg / 1.03 LBS
536 Gs
0.07 kg / 0.15 LBS
70 g / 0.7 N
 0.42 kg / 0.92 LBS
~0 Gs
Two strong neodymiums interact from a much further distance than a magnet and steel setup. Such a system of two magnets produces a massive flux and a wider radius of action. Want to build a solid fastener? Utilize two neodymiums instead of a neodymium and a striker plate. Be careful that when attracting two neodymiums, the collision energy is huge. The levitation is marginally weaker than the connection force, but still impressive.
*Field value between like poles drops to ~0 Gs at the midpoint of the gap (resulting from vector opposition).
Important: Results demonstrate sliding force of dual identical neodymium magnets (friction ~0.15 for Ni-Ni coating).

Table 7: Safety (HSE) (electronics) - warnings
MP 40x20x5 / N38

Object / Device Limit (Gauss) / mT Safe distance
Pacemaker 5 Gs (0.5 mT) 24.0 cm
Hearing aid 10 Gs (1.0 mT) 18.5 cm
Timepiece 20 Gs (2.0 mT) 14.5 cm
Phone / Smartphone 40 Gs (4.0 mT) 11.0 cm
Car key 50 Gs (5.0 mT) 10.5 cm
Payment card 400 Gs (40.0 mT) 4.5 cm
HDD hard drive 600 Gs (60.0 mT) 3.5 cm
A strong magnetic field is a large risk to electronics and medical implants. These magnets generate a field that disrupts operation of sensitive medical devices. Notice: the unseen radiation acts through matter and plastic. Increased vigilance must be taken by people with hearing aids and drug dispensers. Influence will be felt by: mechanical watches, car keys, membranes, and screens. Avoid contact with magnetic cards, hard drives, or sensitive navigation tools.

Table 8: Impact energy (kinetic energy) - warning
MP 40x20x5 / N38

Start from (mm) Speed (km/h) Energy (J) Predicted outcome
10 mm 17.57 km/h
(4.88 m/s)
 0.42 J
30 mm 20.25 km/h
(5.62 m/s)
 0.56 J
50 mm 20.46 km/h
(5.68 m/s)
 0.57 J
100 mm 20.50 km/h
(5.69 m/s)
 0.57 J
Neodymium magnets are prone to chipping – a collision with steel causes immediate chipping. Pay attention to connection velocity – a magnet released freely turns into a projectile. Striking energy can destroy the magnet or dangerous crushing to skin. Hold the magnet firmly during mounting so it doesn't slam with momentum against the metal. A collision at high speed ends with a crack of the neodymium. Use safety goggles when working with large magnets.

Table 9: Surface protection spec
MP 40x20x5 / N38

Technical parameter Value / Description
Coating type [NiCuNi] Nickel
Layer structure Nickel - Copper - Nickel
Layer thickness 10-20 µm
Salt spray test (SST) ? 24 h
Recommended environment Indoors only (dry)
For outdoor applications, an epoxy coating is required; standard nickel is intended for indoor use. The silver nickel coating also serves an aesthetic function but is not fully waterproof.

Table 10: Construction data (Pc)
MP 40x20x5 / N38

Parameter Value SI Unit / Description
Magnetic Flux 56 325 Mx 563.3 µWb
Pc Coefficient 0.80 High (Stable)
Flux value passing through the pole surface. Key data when building generators as well as sensors. Pc value defines the working geometry.

Table 11: Submerged application
MP 40x20x5 / N38

Environment Effective steel pull Effect
Air (land) 7.24 kg Standard
Water (riverbed) 8.29 kg
(+1.05 kg buoyancy gain)
+14.5%
Corrosion warning: Standard nickel requires drying after every contact with moisture; lack of maintenance will lead to rust spots.
Water displaces steel, making heavy objects slightly lighter. Buoyancy helps in lifting finds.

1. Shear force

*Caution: On a vertical surface, the magnet holds just ~20% of its perpendicular strength.

2. Efficiency vs thickness

*Thin steel (e.g. 0.5mm PC case) drastically limits the holding force.

3. Power loss vs temp

*For N38 material, the critical limit is 80°C.

4. Demagnetization curve and operating point (B-H)

chart generated for the permeance coefficient Pc (Permeance Coefficient) = 0.80

This simulation demonstrates the magnetic stability of the selected magnet under specific geometric conditions. The solid red line represents the demagnetization curve (material potential), while the dashed blue line is the load line based on the magnet's geometry. The Pc (Permeance Coefficient), also known as the load line slope, is a dimensionless value that describes the relationship between the magnet's shape and its magnetic stability. The intersection of these two lines (the black dot) is the operating point — it determines the actual magnetic flux density generated by the magnet in this specific configuration. A higher Pc value means the magnet is more 'slender' (tall relative to its area), resulting in a higher operating point and better resistance to irreversible demagnetization caused by external fields or temperature. A value of 0.42 is relatively low (typical for flat magnets), meaning the operating point is closer to the 'knee' of the curve — caution is advised when operating at temperatures near the maximum limit to avoid strength loss.

Engineering data and GPSR

Elemental analysis

iron (Fe) 64% – 68%
neodymium (Nd) 29% – 32%
boron (B) 1.1% – 1.2%
dysprosium (Dy) 0.5% – 2.0%
coating (Ni-Cu-Ni) < 0.05%

Ecology and recycling (GPSR)

recyclability (EoL) 100%
recycled raw materials ~10% (pre-cons)
carbon footprint low / zredukowany
waste code (EWC) 16 02 16
Safety card (GPSR)
responsible entity
Dhit sp. z o.o.
ul. Kościuszki 6A, 05-850 Ożarów Mazowiecki
tel: +48 22 499 98 98 | e-mail: bok@dhit.pl
batch number/type
id: 030199-2026
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Pros as well as cons of neodymium magnets.

Benefits

Apart from their strong magnetism, neodymium magnets have these key benefits:
  • They retain attractive force for nearly ten years – the loss is just ~1% (according to analyses),
  • Magnets very well protect themselves against loss of magnetization caused by foreign field sources,
  • A magnet with a smooth nickel surface has better aesthetics,
  • Magnets are distinguished by exceptionally strong magnetic induction on the surface,
  • Due to their durability and thermal resistance, neodymium magnets can operate (depending on the shape) even at high temperatures reaching 230°C or more...
  • Possibility of accurate modeling as well as adjusting to defined requirements,
  • Key role in electronics industry – they are used in mass storage devices, motor assemblies, medical equipment, also multitasking production systems.
  • Relatively small size with high pulling force – neodymium magnets offer impressive pulling force in tiny dimensions, which allows their use in small systems

Disadvantages

Cons of neodymium magnets and ways of using them
  • Brittleness is one of their disadvantages. Upon intense impact they can fracture. We advise keeping them in a special holder, which not only secures them against impacts but also raises their durability
  • NdFeB magnets demagnetize when exposed to high temperatures. After reaching 80°C, many of them experience permanent weakening of strength (a factor is the shape and dimensions of the magnet). We offer magnets specially adapted to work at temperatures up to 230°C marked [AH], which are extremely resistant to heat
  • When exposed to humidity, magnets start to rust. To use them in conditions outside, it is recommended to use protective magnets, such as magnets in rubber or plastics, which secure oxidation as well as corrosion.
  • Limited ability of making threads in the magnet and complicated shapes - recommended is cover - magnet mounting.
  • Health risk to health – tiny shards of magnets are risky, in case of ingestion, which gains importance in the context of child health protection. Furthermore, small components of these products can disrupt the diagnostic process medical after entering the body.
  • Due to complex production process, their price is higher than average,

Holding force characteristics

Breakaway strength of the magnet in ideal conditions – what affects it?

The force parameter is a theoretical maximum value performed under the following configuration:
  • with the application of a sheet made of low-carbon steel, ensuring maximum field concentration
  • whose thickness is min. 10 mm
  • with an ideally smooth contact surface
  • without any air gap between the magnet and steel
  • for force applied at a right angle (pull-off, not shear)
  • in neutral thermal conditions

Determinants of lifting force in real conditions

Holding efficiency is influenced by working environment parameters, including (from priority):
  • Clearance – existence of any layer (rust, dirt, air) interrupts the magnetic circuit, which lowers power rapidly (even by 50% at 0.5 mm).
  • Direction of force – highest force is available only during perpendicular pulling. The shear force of the magnet along the surface is usually many times lower (approx. 1/5 of the lifting capacity).
  • Metal thickness – the thinner the sheet, the weaker the hold. Part of the magnetic field penetrates through instead of converting into lifting capacity.
  • Material type – the best choice is high-permeability steel. Stainless steels may have worse magnetic properties.
  • Smoothness – full contact is obtained only on smooth steel. Rough texture create air cushions, weakening the magnet.
  • Temperature influence – hot environment reduces magnetic field. Too high temperature can permanently demagnetize the magnet.

Lifting capacity was measured by applying a steel plate with a smooth surface of optimal thickness (min. 20 mm), under vertically applied force, whereas under parallel forces the lifting capacity is smaller. Additionally, even a small distance between the magnet’s surface and the plate reduces the lifting capacity.

Safety rules for work with neodymium magnets
Warning for allergy sufferers

Nickel alert: The Ni-Cu-Ni coating consists of nickel. If redness appears, immediately stop working with magnets and wear gloves.

Keep away from computers

Data protection: Neodymium magnets can ruin data carriers and delicate electronics (heart implants, hearing aids, timepieces).

Serious injuries

Large magnets can break fingers in a fraction of a second. Under no circumstances put your hand between two attracting surfaces.

Immense force

Handle with care. Neodymium magnets act from a distance and connect with massive power, often quicker than you can move away.

Fire warning

Drilling and cutting of NdFeB material poses a fire hazard. Magnetic powder oxidizes rapidly with oxygen and is difficult to extinguish.

Do not overheat magnets

Regular neodymium magnets (grade N) undergo demagnetization when the temperature surpasses 80°C. Damage is permanent.

Choking Hazard

These products are not intended for children. Eating several magnets can lead to them pinching intestinal walls, which poses a severe health hazard and requires immediate surgery.

ICD Warning

For implant holders: Strong magnetic fields disrupt electronics. Maintain at least 30 cm distance or request help to work with the magnets.

Eye protection

Despite metallic appearance, the material is delicate and not impact-resistant. Avoid impacts, as the magnet may shatter into sharp, dangerous pieces.

Keep away from electronics

Remember: rare earth magnets produce a field that interferes with precision electronics. Keep a separation from your mobile, device, and navigation systems.

Attention! Looking for details? Check our post: Why are neodymium magnets dangerous?