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MP 20x8/4x5 / N38 - ring magnet

ring magnet

Catalog no 030333

GTIN/EAN: 5906301812272

5.00
Load capacity 6.65 kg / 65.21 N Magnetic Induction 277.16 mT / 2772 Gs
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
Coating
[NiCuNi] Nickel

7.75 with VAT / pcs + price for transport

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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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Lifting power along with appearance of a neodymium magnet can be analyzed using our force calculator.

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Detailed specification - 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 simulation of the product - data

Presented values constitute the direct effect of a mathematical analysis. Values rely on models for the class Nd2Fe14B. Real-world conditions might slightly differ. Please consider these data as a reference point for designers.

Table 1: Static pull force (pull 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 lbs
6650.0 g / 65.2 N
medium risk
1 mm 2265 Gs
226.5 mT
5.81 kg / 12.80 lbs
5807.9 g / 57.0 N
medium risk
2 mm 2070 Gs
207.0 mT
4.85 kg / 10.69 lbs
4851.0 g / 47.6 N
medium risk
3 mm 1858 Gs
185.8 mT
3.91 kg / 8.61 lbs
3906.5 g / 38.3 N
medium risk
5 mm 1437 Gs
143.7 mT
2.34 kg / 5.16 lbs
2338.7 g / 22.9 N
medium risk
10 mm 691 Gs
69.1 mT
0.54 kg / 1.19 lbs
540.5 g / 5.3 N
safe
15 mm 343 Gs
34.3 mT
0.13 kg / 0.29 lbs
133.3 g / 1.3 N
safe
20 mm 186 Gs
18.6 mT
0.04 kg / 0.09 lbs
39.3 g / 0.4 N
safe
30 mm 70 Gs
7.0 mT
0.01 kg / 0.01 lbs
5.5 g / 0.1 N
safe
50 mm 18 Gs
1.8 mT
0.00 kg / 0.00 lbs
0.4 g / 0.0 N
safe

Table 2: Shear load (vertical surface)
MP 20x8/4x5 / N38

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

Table 3: Wall mounting (sliding) - behavior on slippery surfaces
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 lbs
1995.0 g / 19.6 N
Painted steel (standard)
µ = 0.2 20% Nominalnej Siły
1.33 kg / 2.93 lbs
1330.0 g / 13.0 N
Oily/slippery steel
µ = 0.1 10% Nominalnej Siły
0.67 kg / 1.47 lbs
665.0 g / 6.5 N
Magnet with anti-slip rubber
µ = 0.5 50% Nominalnej Siły
3.33 kg / 7.33 lbs
3325.0 g / 32.6 N

Table 4: Steel thickness (substrate influence) - sheet metal selection
MP 20x8/4x5 / N38

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

Table 5: Thermal stability (stability) - power drop
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 lbs
6650.0 g / 65.2 N
OK
40 °C -2.2% 6.50 kg / 14.34 lbs
6503.7 g / 63.8 N
OK
60 °C -4.4% 6.36 kg / 14.02 lbs
6357.4 g / 62.4 N
80 °C -6.6% 6.21 kg / 13.69 lbs
6211.1 g / 60.9 N
100 °C -28.8% 4.73 kg / 10.44 lbs
4734.8 g / 46.4 N

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

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

Table 7: Safety (HSE) (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: Dynamics (kinetic energy) - warning
MP 20x8/4x5 / N38

Start from (mm) Speed (km/h) Energy (J) Predicted outcome
10 mm 25.22 km/h
(7.01 m/s)
0.28 J
30 mm 26.09 km/h
(7.25 m/s)
0.30 J
50 mm 26.10 km/h
(7.25 m/s)
0.30 J
100 mm 26.11 km/h
(7.25 m/s)
0.30 J

Table 9: Anti-corrosion coating durability
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: Construction data (Pc)
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: Underwater work (magnet fishing)
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: This magnet has a standard nickel coating. After use in water, it must be dried and maintained immediately, otherwise it will rust!

1. Shear force

*Warning: On a vertical wall, the magnet holds just ~20% of its max power.

2. Plate thickness effect

*Thin metal sheet (e.g. computer case) significantly weakens the holding force.

3. Temperature resistance

*For standard magnets, 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.

Technical specification and ecology

Chemical composition

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

Force (pull)


Magnetic Induction

Other deals

It is ideally suited for places where solid attachment of the magnet to the substrate is required without the risk of detachment. 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. When tightening the screw, you must maintain great sensitivity. We recommend tightening manually with a screwdriver, not an impact driver, because excessive force will cause the ring to crack. It's a good idea to use a flexible washer under the screw head, which will cushion the stresses. 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 does not ensure full waterproofing. 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. If you must use it outside, paint it with anti-corrosion paint after mounting.
A screw or bolt with a thread diameter smaller than 8/4 mm fits this model. For magnets with a straight hole, a conical head can act like a wedge and burst the magnet. Aesthetic mounting requires selecting the appropriate head size.
This model is characterized by dimensions Ø20x5 mm and a weight of 11.31 g. The key parameter here is the holding force amounting to approximately 6.65 kg (force ~65.21 N). The mounting hole diameter is precisely 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 and weaknesses of Nd2Fe14B magnets.

Benefits

In addition to their magnetic efficiency, neodymium magnets provide the following advantages:
  • They have constant strength, and over more than ten years their attraction force decreases symbolically – ~1% (in testing),
  • They retain their magnetic properties even under strong external field,
  • Thanks to the elegant finish, the layer of nickel, gold, or silver gives an clean appearance,
  • Magnets are characterized by maximum magnetic induction on the outer side,
  • Through (appropriate) combination of ingredients, they can achieve high thermal strength, enabling action at temperatures reaching 230°C and above...
  • Possibility of precise creating as well as adapting to individual applications,
  • Universal use in advanced technology sectors – they are used in HDD drives, electric motors, diagnostic systems, as well as technologically advanced constructions.
  • Thanks to their power density, small magnets offer high operating force, with minimal size,

Limitations

Disadvantages of neodymium magnets:
  • To avoid cracks under impact, we recommend using special steel holders. Such a solution protects the magnet and simultaneously increases its durability.
  • Neodymium magnets lose their strength under the influence of heating. As soon as 80°C is exceeded, many of them start losing their power. Therefore, we recommend our special magnets marked [AH], which maintain durability even at temperatures up to 230°C
  • Magnets exposed to a humid environment can corrode. Therefore while using outdoors, we advise using waterproof magnets made of rubber, plastic or other material resistant to moisture
  • Limited ability of making threads in the magnet and complex forms - preferred is a housing - mounting mechanism.
  • Health risk resulting from small fragments of magnets can be dangerous, when accidentally swallowed, which gains importance in the context of child health protection. It is also worth noting that small elements of these devices can disrupt the diagnostic process medical when they are in the body.
  • Due to neodymium price, their price is higher than average,

Pull force analysis

Highest magnetic holding forcewhat it depends on?

The specified lifting capacity represents the peak performance, obtained under ideal test conditions, namely:
  • on a plate made of structural steel, perfectly concentrating the magnetic flux
  • with a thickness of at least 10 mm
  • characterized by lack of roughness
  • without any clearance between the magnet and steel
  • during detachment in a direction perpendicular to the mounting surface
  • at temperature approx. 20 degrees Celsius

Magnet lifting force in use – key factors

Holding efficiency impacted by specific conditions, including (from priority):
  • Distance – the presence of foreign body (paint, tape, gap) interrupts the magnetic circuit, which reduces power rapidly (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.
  • Steel thickness – insufficiently thick plate does not close the flux, causing part of the power to be escaped into the air.
  • Chemical composition of the base – low-carbon steel gives the best results. Alloy steels decrease magnetic properties and holding force.
  • Smoothness – ideal contact is possible only on polished steel. Rough texture reduce the real contact area, reducing force.
  • Thermal factor – hot environment weakens pulling force. Exceeding the limit temperature can permanently damage the magnet.

Holding force was tested on the plate surface of 20 mm thickness, when a perpendicular force was applied, whereas under parallel forces the load capacity is reduced by as much as 75%. In addition, even a minimal clearance between the magnet’s surface and the plate decreases the holding force.

Warnings
Machining danger

Combustion risk: Neodymium dust is highly flammable. Avoid machining magnets without safety gear as this may cause fire.

Safe operation

Exercise caution. Neodymium magnets attract from a long distance and connect with massive power, often faster than you can react.

Metal Allergy

It is widely known that nickel (standard magnet coating) is a strong allergen. If your skin reacts to metals, prevent touching magnets with bare hands or opt for encased magnets.

Fragile material

Despite the nickel coating, neodymium is brittle and not impact-resistant. Do not hit, as the magnet may crumble into sharp, dangerous pieces.

Cards and drives

Very strong magnetic fields can destroy records on payment cards, hard drives, and storage devices. Stay away of at least 10 cm.

Permanent damage

Control the heat. Heating the magnet to high heat will destroy its magnetic structure and strength.

Crushing risk

Protect your hands. Two large magnets will join instantly with a force of several hundred kilograms, crushing everything in their path. Exercise extreme caution!

Keep away from children

NdFeB magnets are not suitable for play. Swallowing a few magnets can lead to them attracting across intestines, which constitutes a severe health hazard and requires immediate surgery.

Threat to navigation

Be aware: rare earth magnets generate a field that disrupts sensitive sensors. Keep a safe distance from your phone, device, and navigation systems.

Life threat

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

Important! Learn more about risks in the article: Magnet Safety Guide.