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MP 20x8/4x3 / N38 - ring magnet

ring magnet

Catalog no 030187

GTIN/EAN: 5906301812043

5.00

Diameter

20 mm [±0,1 mm]

internal diameter Ø

8/4 mm [±0,1 mm]

Height

3 mm [±0,1 mm]

Weight

6.79 g

Magnetization Direction

↑ axial

Load capacity

3.14 kg / 30.79 N

Magnetic Induction

178.11 mT / 1781 Gs

Coating

[NiCuNi] Nickel

3.59 with VAT / pcs + price for transport

2.92 ZŁ net + 23% VAT / pcs

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Technical data - MP 20x8/4x3 / N38 - ring magnet

Specification / characteristics - MP 20x8/4x3 / N38 - ring magnet

properties
properties values
Cat. no. 030187
GTIN/EAN 5906301812043
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 3 mm [±0,1 mm]
Weight 6.79 g
Magnetization Direction ↑ axial
Load capacity ~ ? 3.14 kg / 30.79 N
Magnetic Induction ~ ? 178.11 mT / 1781 Gs
Coating [NiCuNi] Nickel
Manufacturing Tolerance ±0.1 mm

Magnetic properties of material N38

Specification / characteristics MP 20x8/4x3 / 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

Engineering modeling of the product - data

The following information represent the outcome of a engineering simulation. Values were calculated on algorithms for the class Nd2Fe14B. Actual parameters might slightly differ from theoretical values. Treat these data as a preliminary roadmap when designing systems.

Table 1: Static pull force (force vs gap) - interaction chart
MP 20x8/4x3 / N38

Distance (mm) Induction (Gauss) / mT Pull Force (kg/lbs/g/N) Risk Status
0 mm 1531 Gs
153.1 mT
3.14 kg / 6.92 pounds
3140.0 g / 30.8 N
medium risk
1 mm 1457 Gs
145.7 mT
2.84 kg / 6.27 pounds
2843.2 g / 27.9 N
medium risk
2 mm 1352 Gs
135.2 mT
2.45 kg / 5.39 pounds
2446.6 g / 24.0 N
medium risk
3 mm 1227 Gs
122.7 mT
2.02 kg / 4.44 pounds
2016.2 g / 19.8 N
medium risk
5 mm 963 Gs
96.3 mT
1.24 kg / 2.74 pounds
1241.9 g / 12.2 N
low risk
10 mm 465 Gs
46.5 mT
0.29 kg / 0.64 pounds
289.3 g / 2.8 N
low risk
15 mm 228 Gs
22.8 mT
0.07 kg / 0.15 pounds
69.7 g / 0.7 N
low risk
20 mm 122 Gs
12.2 mT
0.02 kg / 0.04 pounds
20.0 g / 0.2 N
low risk
30 mm 45 Gs
4.5 mT
0.00 kg / 0.01 pounds
2.7 g / 0.0 N
low risk
50 mm 11 Gs
1.1 mT
0.00 kg / 0.00 pounds
0.2 g / 0.0 N
low risk

Table 2: Slippage hold (vertical surface)
MP 20x8/4x3 / N38

Distance (mm) Friction coefficient Pull Force (kg/lbs/g/N)
0 mm Stal (~0.2) 0.63 kg / 1.38 pounds
628.0 g / 6.2 N
1 mm Stal (~0.2) 0.57 kg / 1.25 pounds
568.0 g / 5.6 N
2 mm Stal (~0.2) 0.49 kg / 1.08 pounds
490.0 g / 4.8 N
3 mm Stal (~0.2) 0.40 kg / 0.89 pounds
404.0 g / 4.0 N
5 mm Stal (~0.2) 0.25 kg / 0.55 pounds
248.0 g / 2.4 N
10 mm Stal (~0.2) 0.06 kg / 0.13 pounds
58.0 g / 0.6 N
15 mm Stal (~0.2) 0.01 kg / 0.03 pounds
14.0 g / 0.1 N
20 mm Stal (~0.2) 0.00 kg / 0.01 pounds
4.0 g / 0.0 N
30 mm Stal (~0.2) 0.00 kg / 0.00 pounds
0.0 g / 0.0 N
50 mm Stal (~0.2) 0.00 kg / 0.00 pounds
0.0 g / 0.0 N

Table 3: Wall mounting (sliding) - behavior on slippery surfaces
MP 20x8/4x3 / N38

Surface type Friction coefficient / % Mocy Max load (kg/lbs/g/N)
Raw steel
µ = 0.3 30% Nominalnej Siły
0.94 kg / 2.08 pounds
942.0 g / 9.2 N
Painted steel (standard)
µ = 0.2 20% Nominalnej Siły
0.63 kg / 1.38 pounds
628.0 g / 6.2 N
Oily/slippery steel
µ = 0.1 10% Nominalnej Siły
0.31 kg / 0.69 pounds
314.0 g / 3.1 N
Magnet with anti-slip rubber
µ = 0.5 50% Nominalnej Siły
1.57 kg / 3.46 pounds
1570.0 g / 15.4 N

Table 4: Material efficiency (saturation) - sheet metal selection
MP 20x8/4x3 / N38

Steel thickness (mm) % power Real pull force (kg/lbs/g/N)
0.5 mm
10%
0.31 kg / 0.69 pounds
314.0 g / 3.1 N
1 mm
25%
0.79 kg / 1.73 pounds
785.0 g / 7.7 N
2 mm
50%
1.57 kg / 3.46 pounds
1570.0 g / 15.4 N
3 mm
75%
2.36 kg / 5.19 pounds
2355.0 g / 23.1 N
5 mm
100%
3.14 kg / 6.92 pounds
3140.0 g / 30.8 N
10 mm
100%
3.14 kg / 6.92 pounds
3140.0 g / 30.8 N
11 mm
100%
3.14 kg / 6.92 pounds
3140.0 g / 30.8 N
12 mm
100%
3.14 kg / 6.92 pounds
3140.0 g / 30.8 N

Table 5: Working in heat (stability) - power drop
MP 20x8/4x3 / N38

Ambient temp. (°C) Power loss Remaining pull (kg/lbs/g/N) Status
20 °C 0.0% 3.14 kg / 6.92 pounds
3140.0 g / 30.8 N
OK
40 °C -2.2% 3.07 kg / 6.77 pounds
3070.9 g / 30.1 N
OK
60 °C -4.4% 3.00 kg / 6.62 pounds
3001.8 g / 29.4 N
80 °C -6.6% 2.93 kg / 6.47 pounds
2932.8 g / 28.8 N
100 °C -28.8% 2.24 kg / 4.93 pounds
2235.7 g / 21.9 N

Table 6: Magnet-Magnet interaction (repulsion) - field collision
MP 20x8/4x3 / N38

Gap (mm) Attraction (kg/lbs) (N-S) Shear Strength (kg/lbs/g/N) Repulsion (kg/lbs) (N-N)
0 mm 3.71 kg / 8.17 pounds
2 815 Gs
0.56 kg / 1.23 pounds
556 g / 5.5 N
N/A
1 mm 3.55 kg / 7.83 pounds
2 998 Gs
0.53 kg / 1.17 pounds
533 g / 5.2 N
3.20 kg / 7.05 pounds
~0 Gs
2 mm 3.36 kg / 7.40 pounds
2 915 Gs
0.50 kg / 1.11 pounds
503 g / 4.9 N
3.02 kg / 6.66 pounds
~0 Gs
3 mm 3.13 kg / 6.90 pounds
2 815 Gs
0.47 kg / 1.04 pounds
470 g / 4.6 N
2.82 kg / 6.21 pounds
~0 Gs
5 mm 2.63 kg / 5.81 pounds
2 582 Gs
0.40 kg / 0.87 pounds
395 g / 3.9 N
2.37 kg / 5.23 pounds
~0 Gs
10 mm 1.47 kg / 3.23 pounds
1 926 Gs
0.22 kg / 0.48 pounds
220 g / 2.2 N
1.32 kg / 2.91 pounds
~0 Gs
20 mm 0.34 kg / 0.75 pounds
930 Gs
0.05 kg / 0.11 pounds
51 g / 0.5 N
0.31 kg / 0.68 pounds
~0 Gs
50 mm 0.01 kg / 0.02 pounds
143 Gs
0.00 kg / 0.00 pounds
1 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
60 mm 0.00 kg / 0.01 pounds
90 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
70 mm 0.00 kg / 0.00 pounds
59 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs
80 mm 0.00 kg / 0.00 pounds
41 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
30 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
22 Gs
0.00 kg / 0.00 pounds
0 g / 0.0 N
0.00 kg / 0.00 pounds
~0 Gs

Table 7: Safety (HSE) (implants) - warnings
MP 20x8/4x3 / N38

Object / Device Limit (Gauss) / mT Safe distance
Pacemaker 5 Gs (0.5 mT) 7.0 cm
Hearing aid 10 Gs (1.0 mT) 5.5 cm
Mechanical watch 20 Gs (2.0 mT) 4.5 cm
Phone / Smartphone 40 Gs (4.0 mT) 3.5 cm
Car key 50 Gs (5.0 mT) 3.0 cm
Payment card 400 Gs (40.0 mT) 1.5 cm
HDD hard drive 600 Gs (60.0 mT) 1.0 cm

Table 8: Dynamics (kinetic energy) - warning
MP 20x8/4x3 / N38

Start from (mm) Speed (km/h) Energy (J) Predicted outcome
10 mm 22.90 km/h
(6.36 m/s)
0.14 J
30 mm 37.58 km/h
(10.44 m/s)
0.37 J
50 mm 48.50 km/h
(13.47 m/s)
0.62 J
100 mm 68.58 km/h
(19.05 m/s)
1.23 J

Table 9: Anti-corrosion coating durability
MP 20x8/4x3 / 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 (Pc)
MP 20x8/4x3 / N38

Parameter Value SI Unit / Description
Magnetic Flux 5 044 Mx 50.4 µWb
Pc Coefficient 0.20 Low (Flat)

Table 11: Hydrostatics and buoyancy
MP 20x8/4x3 / N38

Environment Effective steel pull Effect
Air (land) 3.14 kg Standard
Water (riverbed) 3.60 kg
(+0.46 kg buoyancy gain)
+14.5%
Warning: Standard nickel requires drying after every contact with moisture; lack of maintenance will lead to rust spots.
1. Vertical hold

*Caution: On a vertical wall, the magnet retains merely approx. 20-30% of its max power.

2. Steel thickness impact

*Thin steel (e.g. computer case) drastically weakens the holding force.

3. Temperature resistance

*For standard magnets, the safety limit is 80°C.

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

chart generated for the permeance coefficient Pc (Permeance Coefficient) = 0.20

The chart above illustrates the magnetic characteristics of the material within the second quadrant of the hysteresis loop. 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.

Technical specification and ecology
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%
Sustainability
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: 030187-2026
Measurement Calculator
Magnet pull force

Field Strength

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The ring-shaped magnet MP 20x8/4x3 / 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.
These magnets are coated with standard Ni-Cu-Ni plating, which protects them in indoor conditions, but is not sufficient for rain. In the place of the mounting hole, the coating is thinner and easily scratched when tightening the screw, which will become a corrosion focus. This product is dedicated for indoor use. For outdoor applications, we recommend choosing rubberized holders 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.
It is a magnetic ring with a diameter of 20 mm and thickness 3 mm. The pulling force of this model is an impressive 3.14 kg, which translates to 30.79 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. If you want two such magnets screwed with cones facing each other (faces) to attract, you must connect them with opposite poles (N to S). We do not offer paired sets with marked poles in this category, but they are easy to match manually.

Advantages as well as disadvantages of neodymium magnets.

Benefits

Apart from their consistent holding force, neodymium magnets have these key benefits:
  • They virtually do not lose strength, because even after ten years the decline in efficiency is only ~1% (according to literature),
  • They feature excellent resistance to weakening of magnetic properties as a result of external magnetic sources,
  • By covering with a shiny coating of nickel, the element acquires an modern look,
  • They are known for high magnetic induction at the operating surface, which increases their power,
  • Neodymium magnets are characterized by very high magnetic induction on the magnet surface and can function (depending on the shape) even at a temperature of 230°C or more...
  • Possibility of detailed modeling as well as optimizing to individual needs,
  • Key role in modern industrial fields – they are commonly used in mass storage devices, drive modules, diagnostic systems, and complex engineering applications.
  • Compactness – despite small sizes they generate large force, making them ideal for precision applications

Weaknesses

Disadvantages of NdFeB magnets:
  • To avoid cracks under impact, we recommend using special steel holders. Such a solution secures the magnet and simultaneously improves its durability.
  • When exposed to high temperature, neodymium magnets experience a drop in strength. 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
  • Magnets exposed to a humid environment can corrode. Therefore while using outdoors, we recommend using waterproof magnets made of rubber, plastic or other material protecting against moisture
  • Limited possibility of producing threads in the magnet and complicated forms - preferred is cover - magnet mounting.
  • Health risk resulting from small fragments of magnets pose a threat, when accidentally swallowed, which gains importance in the context of child health protection. It is also worth noting that tiny parts of these products are able to disrupt the diagnostic process medical when they are in the body.
  • Due to expensive raw materials, their price is relatively high,

Holding force characteristics

Detachment force of the magnet in optimal conditionswhat contributes to it?

The lifting capacity listed is a theoretical maximum value performed under the following configuration:
  • on a block made of mild steel, perfectly concentrating the magnetic flux
  • whose thickness is min. 10 mm
  • characterized by even structure
  • under conditions of no distance (metal-to-metal)
  • under perpendicular force vector (90-degree angle)
  • at ambient temperature room level

Determinants of practical lifting force of a magnet

Bear in mind that the magnet holding may be lower depending on elements below, in order of importance:
  • Gap between surfaces – even a fraction of a millimeter of distance (caused e.g. by varnish or dirt) drastically reduces the magnet efficiency, often by half at just 0.5 mm.
  • Load vector – maximum parameter is obtained only during pulling at a 90° angle. The resistance to sliding of the magnet along the surface is standardly several times lower (approx. 1/5 of the lifting capacity).
  • Wall thickness – the thinner the sheet, the weaker the hold. Magnetic flux passes through the material instead of generating force.
  • Steel type – mild steel attracts best. Higher carbon content reduce magnetic permeability and lifting capacity.
  • Surface finish – full contact is possible only on smooth steel. Any scratches and bumps create air cushions, weakening the magnet.
  • Temperature – heating the magnet results in weakening of induction. It is worth remembering the thermal limit for a given model.

Lifting capacity testing was carried out on a smooth plate of suitable thickness, under a perpendicular pulling force, whereas under attempts to slide the magnet the lifting capacity is smaller. Moreover, even a minimal clearance between the magnet and the plate reduces the holding force.

H&S for magnets
Powerful field

Handle magnets with awareness. Their powerful strength can shock even experienced users. Stay alert and do not underestimate their power.

Threat to navigation

A powerful magnetic field negatively affects the functioning of magnetometers in smartphones and navigation systems. Maintain magnets near a smartphone to avoid damaging the sensors.

Bodily injuries

Protect your hands. Two powerful magnets will join immediately with a force of massive weight, destroying everything in their path. Exercise extreme caution!

Magnetic media

Device Safety: Strong magnets can ruin payment cards and delicate electronics (heart implants, medical aids, timepieces).

Keep away from children

Product intended for adults. Tiny parts can be swallowed, causing serious injuries. Store out of reach of kids and pets.

Dust explosion hazard

Machining of NdFeB material poses a fire hazard. Neodymium dust reacts violently with oxygen and is hard to extinguish.

Health Danger

Medical warning: Strong magnets can turn off heart devices and defibrillators. Do not approach if you have medical devices.

Beware of splinters

Despite the nickel coating, the material is brittle and not impact-resistant. Avoid impacts, as the magnet may crumble into sharp, dangerous pieces.

Permanent damage

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

Nickel coating and allergies

Medical facts indicate that the nickel plating (standard magnet coating) is a potent allergen. For allergy sufferers, avoid direct skin contact or select encased magnets.

Important! Looking for details? Check our post: Are neodymium magnets dangerous?