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MP 20x8/4x5 / N38 - ring magnet

ring magnet

Catalog no 030333

GTIN/EAN: 5906301812272

5.00

Diameter

20 mm [±0,1 mm]

internal diameter Ø

8/4 mm [±0,1 mm]

Height

5 mm [±0,1 mm]

Weight

11.31 g

Magnetization Direction

↑ axial

Load capacity

6.65 kg / 65.21 N

Magnetic Induction

277.16 mT / 2772 Gs

Coating

[NiCuNi] Nickel

7.75 with VAT / pcs + price for transport

6.30 ZŁ net + 23% VAT / pcs

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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.

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Technical details - MP 20x8/4x5 / N38 - ring magnet

Specification / characteristics - MP 20x8/4x5 / N38 - ring magnet

properties
properties values
Cat. no. 030333
GTIN/EAN 5906301812272
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 20 mm [±0,1 mm]
internal diameter Ø 8/4 mm [±0,1 mm]
Height 5 mm [±0,1 mm]
Weight 11.31 g
Magnetization Direction ↑ axial
Load capacity ~ ? 6.65 kg / 65.21 N
Magnetic Induction ~ ? 277.16 mT / 2772 Gs
Coating [NiCuNi] Nickel
Manufacturing Tolerance ±0.1 mm

Magnetic properties of material N38

Specification / characteristics MP 20x8/4x5 / N38 - ring magnet
properties values units
remenance Br [min. - max.] ? 12.2-12.6 kGs
remenance Br [min. - max.] ? 1220-1260 mT
coercivity bHc ? 10.8-11.5 kOe
coercivity bHc ? 860-915 kA/m
actual internal force iHc ≥ 12 kOe
actual internal force iHc ≥ 955 kA/m
energy density [min. - max.] ? 36-38 BH max MGOe
energy density [min. - max.] ? 287-303 BH max KJ/m
max. 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 312 - 380 °C
Curie Temperature TF 593 - 716 °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

Physical modeling of the magnet - report

The following information are the direct effect of a mathematical calculation. Results are based on models for the class Nd2Fe14B. Real-world parameters may differ. Use these calculations as a preliminary roadmap during assembly planning.

Table 1: Static force (force vs gap) - characteristics
MP 20x8/4x5 / N38

Distance (mm) Induction (Gauss) / mT Pull Force (kg/lbs/g/N) Risk Status
0 mm 2424 Gs
242.4 mT
6.65 kg / 14.66 pounds
6650.0 g / 65.2 N
strong
1 mm 2265 Gs
226.5 mT
5.81 kg / 12.80 pounds
5807.9 g / 57.0 N
strong
2 mm 2070 Gs
207.0 mT
4.85 kg / 10.69 pounds
4851.0 g / 47.6 N
strong
3 mm 1858 Gs
185.8 mT
3.91 kg / 8.61 pounds
3906.5 g / 38.3 N
strong
5 mm 1437 Gs
143.7 mT
2.34 kg / 5.16 pounds
2338.7 g / 22.9 N
strong
10 mm 691 Gs
69.1 mT
0.54 kg / 1.19 pounds
540.5 g / 5.3 N
weak grip
15 mm 343 Gs
34.3 mT
0.13 kg / 0.29 pounds
133.3 g / 1.3 N
weak grip
20 mm 186 Gs
18.6 mT
0.04 kg / 0.09 pounds
39.3 g / 0.4 N
weak grip
30 mm 70 Gs
7.0 mT
0.01 kg / 0.01 pounds
5.5 g / 0.1 N
weak grip
50 mm 18 Gs
1.8 mT
0.00 kg / 0.00 pounds
0.4 g / 0.0 N
weak grip

Table 2: Vertical capacity (wall)
MP 20x8/4x5 / N38

Distance (mm) Friction coefficient Pull Force (kg/lbs/g/N)
0 mm Stal (~0.2) 1.33 kg / 2.93 pounds
1330.0 g / 13.0 N
1 mm Stal (~0.2) 1.16 kg / 2.56 pounds
1162.0 g / 11.4 N
2 mm Stal (~0.2) 0.97 kg / 2.14 pounds
970.0 g / 9.5 N
3 mm Stal (~0.2) 0.78 kg / 1.72 pounds
782.0 g / 7.7 N
5 mm Stal (~0.2) 0.47 kg / 1.03 pounds
468.0 g / 4.6 N
10 mm Stal (~0.2) 0.11 kg / 0.24 pounds
108.0 g / 1.1 N
15 mm Stal (~0.2) 0.03 kg / 0.06 pounds
26.0 g / 0.3 N
20 mm Stal (~0.2) 0.01 kg / 0.02 pounds
8.0 g / 0.1 N
30 mm Stal (~0.2) 0.00 kg / 0.00 pounds
2.0 g / 0.0 N
50 mm Stal (~0.2) 0.00 kg / 0.00 pounds
0.0 g / 0.0 N

Table 3: Vertical assembly (shearing) - vertical pull
MP 20x8/4x5 / N38

Surface type Friction coefficient / % Mocy Max load (kg/lbs/g/N)
Raw steel
µ = 0.3 30% Nominalnej Siły
2.00 kg / 4.40 pounds
1995.0 g / 19.6 N
Painted steel (standard)
µ = 0.2 20% Nominalnej Siły
1.33 kg / 2.93 pounds
1330.0 g / 13.0 N
Oily/slippery steel
µ = 0.1 10% Nominalnej Siły
0.67 kg / 1.47 pounds
665.0 g / 6.5 N
Magnet with anti-slip rubber
µ = 0.5 50% Nominalnej Siły
3.33 kg / 7.33 pounds
3325.0 g / 32.6 N

Table 4: Steel thickness (saturation) - power losses
MP 20x8/4x5 / N38

Steel thickness (mm) % power Real pull force (kg/lbs/g/N)
0.5 mm
10%
0.67 kg / 1.47 pounds
665.0 g / 6.5 N
1 mm
25%
1.66 kg / 3.67 pounds
1662.5 g / 16.3 N
2 mm
50%
3.33 kg / 7.33 pounds
3325.0 g / 32.6 N
3 mm
75%
4.99 kg / 11.00 pounds
4987.5 g / 48.9 N
5 mm
100%
6.65 kg / 14.66 pounds
6650.0 g / 65.2 N
10 mm
100%
6.65 kg / 14.66 pounds
6650.0 g / 65.2 N
11 mm
100%
6.65 kg / 14.66 pounds
6650.0 g / 65.2 N
12 mm
100%
6.65 kg / 14.66 pounds
6650.0 g / 65.2 N

Table 5: Thermal resistance (material behavior) - thermal limit
MP 20x8/4x5 / N38

Ambient temp. (°C) Power loss Remaining pull (kg/lbs/g/N) Status
20 °C 0.0% 6.65 kg / 14.66 pounds
6650.0 g / 65.2 N
OK
40 °C -2.2% 6.50 kg / 14.34 pounds
6503.7 g / 63.8 N
OK
60 °C -4.4% 6.36 kg / 14.02 pounds
6357.4 g / 62.4 N
80 °C -6.6% 6.21 kg / 13.69 pounds
6211.1 g / 60.9 N
100 °C -28.8% 4.73 kg / 10.44 pounds
4734.8 g / 46.4 N

Table 6: Two magnets (repulsion) - field range
MP 20x8/4x5 / N38

Gap (mm) Attraction (kg/lbs) (N-S) Lateral Force (kg/lbs/g/N) Repulsion (kg/lbs) (N-N)
0 mm 9.28 kg / 20.47 pounds
4 012 Gs
1.39 kg / 3.07 pounds
1393 g / 13.7 N
N/A
1 mm 8.73 kg / 19.25 pounds
4 701 Gs
1.31 kg / 2.89 pounds
1310 g / 12.8 N
7.86 kg / 17.33 pounds
~0 Gs
2 mm 8.11 kg / 17.88 pounds
4 530 Gs
1.22 kg / 2.68 pounds
1216 g / 11.9 N
7.30 kg / 16.09 pounds
~0 Gs
3 mm 7.45 kg / 16.42 pounds
4 342 Gs
1.12 kg / 2.46 pounds
1117 g / 11.0 N
6.70 kg / 14.78 pounds
~0 Gs
5 mm 6.10 kg / 13.45 pounds
3 930 Gs
0.92 kg / 2.02 pounds
915 g / 9.0 N
5.49 kg / 12.11 pounds
~0 Gs
10 mm 3.27 kg / 7.20 pounds
2 875 Gs
0.49 kg / 1.08 pounds
490 g / 4.8 N
2.94 kg / 6.48 pounds
~0 Gs
20 mm 0.75 kg / 1.66 pounds
1 382 Gs
0.11 kg / 0.25 pounds
113 g / 1.1 N
0.68 kg / 1.50 pounds
~0 Gs
50 mm 0.02 kg / 0.04 pounds
220 Gs
0.00 kg / 0.01 pounds
3 g / 0.0 N
0.02 kg / 0.04 pounds
~0 Gs
60 mm 0.01 kg / 0.02 pounds
139 Gs
0.00 kg / 0.00 pounds
1 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
70 mm 0.00 kg / 0.01 pounds
93 Gs
0.00 kg / 0.00 pounds
1 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
80 mm 0.00 kg / 0.00 pounds
65 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
90 mm 0.00 kg / 0.00 pounds
47 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
100 mm 0.00 kg / 0.00 pounds
35 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs

Table 7: Protective zones (electronics) - warnings
MP 20x8/4x5 / N38

Object / Device Limit (Gauss) / mT Safe distance
Pacemaker 5 Gs (0.5 mT) 8.0 cm
Hearing aid 10 Gs (1.0 mT) 6.5 cm
Mechanical watch 20 Gs (2.0 mT) 5.0 cm
Phone / Smartphone 40 Gs (4.0 mT) 4.0 cm
Car key 50 Gs (5.0 mT) 3.5 cm
Payment card 400 Gs (40.0 mT) 1.5 cm
HDD hard drive 600 Gs (60.0 mT) 1.5 cm

Table 8: Collisions (kinetic energy) - collision effects
MP 20x8/4x5 / N38

Start from (mm) Speed (km/h) Energy (J) Predicted outcome
10 mm 25.67 km/h
(7.13 m/s)
0.29 J
30 mm 42.38 km/h
(11.77 m/s)
0.78 J
50 mm 54.68 km/h
(15.19 m/s)
1.30 J
100 mm 77.33 km/h
(21.48 m/s)
2.61 J

Table 9: Surface protection spec
MP 20x8/4x5 / 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)

Table 10: Electrical data (Flux)
MP 20x8/4x5 / N38

Parameter Value SI Unit / Description
Magnetic Flux 7 218 Mx 72.2 µWb
Pc Coefficient 0.31 Low (Flat)

Table 11: Physics of underwater searching
MP 20x8/4x5 / N38

Environment Effective steel pull Effect
Air (land) 6.65 kg Standard
Water (riverbed) 7.61 kg
(+0.96 kg buoyancy gain)
+14.5%
Rust risk: Remember to wipe the magnet thoroughly after removing it from water and apply a protective layer (e.g., oil) to avoid corrosion.
1. Shear force

*Warning: On a vertical surface, the magnet retains just ~20% of its nominal pull.

2. Steel saturation

*Thin metal sheet (e.g. 0.5mm PC case) significantly limits the holding force.

3. Heat tolerance

*For N38 grade, the max working temp is 80°C.

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

chart generated for the permeance coefficient Pc (Permeance Coefficient) = 0.31

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: 030333-2026
Measurement Calculator
Pulling force

Field Strength

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The ring magnet with a hole MP 20x8/4x5 / N38 is created for mechanical fastening, where glue might fail or be insufficient. Mounting is clean and reversible, unlike gluing. It is also often used in advertising for fixing signs and in workshops for organizing tools.
This material behaves more like porcelain than steel, so it doesn't forgive mistakes during mounting. One turn too many can destroy the magnet, so do it slowly. The flat screw head should evenly press the magnet. Remember: cracking during assembly results from material properties, not a product defect.
Moisture can penetrate micro-cracks in the coating and cause oxidation of the magnet. In the place of the mounting hole, the coating is thinner and can be damaged when tightening the screw, which will become a corrosion focus. This product is dedicated for inside building use. For outdoor applications, we recommend choosing magnets in hermetic housing or additional protection with varnish.
The inner hole diameter determines the maximum size of the mounting element. If the magnet does not have a chamfer (cone), we recommend using a screw with a flat or cylindrical head, or possibly using a washer. Aesthetic mounting requires selecting the appropriate head size.
The presented product is a ring magnet with dimensions Ø20 mm (outer diameter) and height 5 mm. The pulling force of this model is an impressive 6.65 kg, which translates to 65.21 N in newtons. The product has a [NiCuNi] coating and is made of NdFeB material. Inner hole dimension: 8/4 mm.
The poles are located on the planes with holes, not on the sides of the ring. In the case of connecting two rings, make sure one is turned the right way. We do not offer paired sets with marked poles in this category, but they are easy to match manually.

Strengths as well as weaknesses of Nd2Fe14B magnets.

Advantages

Besides their immense field intensity, neodymium magnets offer the following advantages:
  • They virtually do not lose power, because even after ten years the decline in efficiency is only ~1% (according to literature),
  • They possess excellent resistance to magnetism drop as a result of opposing magnetic fields,
  • The use of an aesthetic coating of noble metals (nickel, gold, silver) causes the element to be more visually attractive,
  • Magnets have impressive magnetic induction on the outer side,
  • Through (adequate) combination of ingredients, they can achieve high thermal resistance, allowing for functioning at temperatures approaching 230°C and above...
  • Thanks to versatility in constructing and the ability to modify to unusual requirements,
  • Fundamental importance in future technologies – they find application in data components, motor assemblies, diagnostic systems, and modern systems.
  • Relatively small size with high pulling force – neodymium magnets offer high power in small dimensions, which makes them useful in miniature devices

Cons

Cons of neodymium magnets: application proposals
  • They are prone to damage upon heavy impacts. To avoid cracks, it is worth securing magnets using a steel holder. Such protection not only protects the magnet but also increases its resistance to damage
  • When exposed to high temperature, neodymium magnets suffer a drop in power. Often, when the temperature exceeds 80°C, their strength decreases (depending on the size and shape of the magnet). For those who need magnets for extreme conditions, we offer [AH] versions withstanding up to 230°C
  • They rust in a humid environment - during use outdoors we recommend using waterproof magnets e.g. in rubber, plastic
  • Due to limitations in producing threads and complicated shapes in magnets, we recommend using a housing - magnetic mount.
  • Potential hazard related to microscopic parts of magnets can be dangerous, in case of ingestion, which is particularly important in the aspect of protecting the youngest. It is also worth noting that small components of these magnets can complicate diagnosis medical in case of swallowing.
  • High unit price – neodymium magnets have a higher price than other types of magnets (e.g. ferrite), which increases costs of application in large quantities

Pull force analysis

Magnetic strength at its maximum – what affects it?

Holding force of 6.65 kg is a result of laboratory testing conducted under specific, ideal conditions:
  • with the application of a yoke made of special test steel, ensuring full magnetic saturation
  • possessing a massiveness of at least 10 mm to ensure full flux closure
  • characterized by smoothness
  • under conditions of ideal adhesion (surface-to-surface)
  • during detachment in a direction perpendicular to the mounting surface
  • at temperature room level

Determinants of practical lifting force of a magnet

In real-world applications, the real power depends on many variables, presented from crucial:
  • Distance – the presence of foreign body (rust, dirt, gap) acts as an insulator, which lowers power steeply (even by 50% at 0.5 mm).
  • Force direction – remember that the magnet has greatest strength perpendicularly. Under shear forces, the holding force drops drastically, often to levels of 20-30% of the nominal value.
  • Base massiveness – insufficiently thick sheet does not close the flux, causing part of the flux to be wasted to the other side.
  • Steel grade – ideal substrate is pure iron steel. Hardened steels may generate lower lifting capacity.
  • Smoothness – full contact is possible only on polished steel. Rough texture create air cushions, reducing force.
  • Temperature influence – hot environment weakens pulling force. Exceeding the limit temperature can permanently demagnetize the magnet.

Holding force was measured on a smooth steel plate of 20 mm thickness, when a perpendicular force was applied, however under parallel forces the lifting capacity is smaller. Moreover, even a minimal clearance between the magnet and the plate lowers the lifting capacity.

H&S for magnets
Medical interference

Warning for patients: Powerful magnets disrupt medical devices. Keep at least 30 cm distance or ask another person to handle the magnets.

Allergic reactions

Allergy Notice: The Ni-Cu-Ni coating contains nickel. If an allergic reaction appears, immediately stop handling magnets and wear gloves.

Danger to the youngest

These products are not suitable for play. Eating a few magnets may result in them connecting inside the digestive tract, which constitutes a critical condition and necessitates urgent medical intervention.

Combustion hazard

Powder generated during grinding of magnets is combustible. Do not drill into magnets without proper cooling and knowledge.

Heat warning

Standard neodymium magnets (N-type) lose power when the temperature goes above 80°C. The loss of strength is permanent.

Precision electronics

Note: neodymium magnets generate a field that confuses sensitive sensors. Maintain a safe distance from your phone, device, and navigation systems.

Handling rules

Before starting, read the rules. Uncontrolled attraction can destroy the magnet or injure your hand. Be predictive.

Shattering risk

Despite the nickel coating, neodymium is brittle and cannot withstand shocks. Do not hit, as the magnet may crumble into hazardous fragments.

Finger safety

Mind your fingers. Two large magnets will join instantly with a force of several hundred kilograms, crushing anything in their path. Be careful!

Keep away from computers

Do not bring magnets near a purse, laptop, or TV. The magnetic field can permanently damage these devices and wipe information from cards.

Danger! Want to know more? Check our post: Are neodymium magnets dangerous?