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MP 25x8x20 / N38 - ring magnet

Name: Dhit sp. z o.o.
Address: Kościuszki 6A, Ożarów Mazowiecki, Poland, 05-850, PL
Telephone: +48 22 499 98 98
Price range: 1-6500
Rating: 5

ring magnet

Catalog no 030450

GTIN/EAN: 5906301812340

5.00

Diameter

25 mm [±0,1 mm]

internal diameter Ø

8 mm [±0,1 mm]

Height

20 mm [±0,1 mm]

Weight

66.09 g

Magnetization Direction

↑ axial

Load capacity

19.02 kg / 186.54 N

Magnetic Induction

525.50 mT / 5255 Gs

Coating

[NiCuNi] Nickel

41.71 ZŁ with VAT / pcs + price for transport

33.91 ZŁ net + 23% VAT / pcs

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MP 25x8x20 / N38 - ring magnet

Specification / characteristics MP 25x8x20 / N38 - ring magnet

properties

properties	values
Cat. no.	030450
GTIN/EAN	5906301812340
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	25 mm [±0,1 mm]
internal diameter Ø	8 mm [±0,1 mm]
Height	20 mm [±0,1 mm]
Weight	66.09 g
Magnetization Direction	↑ axial
Load capacity ~ ?	19.02 kg / 186.54 N
Magnetic Induction ~ ?	525.50 mT / 5255 Gs
Coating	[NiCuNi] Nickel
Manufacturing Tolerance	±0.1 mm

Magnetic properties of material N38

Specification / characteristics MP 25x8x20 / 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

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 product - report

These values are the direct effect of a physical calculation. Values were calculated on models for the material Nd₂Fe₁₄B. Real-world conditions may differ from theoretical values. Please consider these data as a reference point when designing systems.

Table 1: Static force (force vs gap) - characteristics
MP 25x8x20 / N38

Distance (mm)	Induction (Gauss) / mT	Pull Force (kg)	Risk Status
0 mm	5777 Gs 577.7 mT	19.02 kg / 19020.0 g 186.6 N	dangerous!
1 mm	5310 Gs 531.0 mT	16.07 kg / 16067.7 g 157.6 N	dangerous!
2 mm	4846 Gs 484.6 mT	13.38 kg / 13380.1 g 131.3 N	dangerous!
3 mm	4397 Gs 439.7 mT	11.02 kg / 11019.3 g 108.1 N	dangerous!
5 mm	3576 Gs 357.6 mT	7.29 kg / 7287.1 g 71.5 N	medium risk
10 mm	2073 Gs 207.3 mT	2.45 kg / 2448.1 g 24.0 N	medium risk
15 mm	1231 Gs 123.1 mT	0.86 kg / 863.8 g 8.5 N	low risk
20 mm	773 Gs 77.3 mT	0.34 kg / 340.1 g 3.3 N	low risk
30 mm	356 Gs 35.6 mT	0.07 kg / 72.1 g 0.7 N	low risk
50 mm	115 Gs 11.5 mT	0.01 kg / 7.5 g 0.1 N	low risk

Magnetic force decreases sharply with every subsequent millimeter of gap. Keep in mind that even a very thin break (e.g., dirt, varnish, veneer) significantly weakens the grip. Neodymiums work most effectively during direct contact; gap drastically cuts the power. Analyze how rapidly the load capacity drop, when the product does not touch flatly to the metal substrate. When designing the arrangement, eliminate unnecessary gaps.

Table 2: Slippage load (vertical surface)
MP 25x8x20 / N38

Distance (mm)	Friction coefficient	Pull Force (kg)
0 mm	Stal (~0.2)	3.80 kg / 3804.0 g 37.3 N
1 mm	Stal (~0.2)	3.21 kg / 3214.0 g 31.5 N
2 mm	Stal (~0.2)	2.68 kg / 2676.0 g 26.3 N
3 mm	Stal (~0.2)	2.20 kg / 2204.0 g 21.6 N
5 mm	Stal (~0.2)	1.46 kg / 1458.0 g 14.3 N
10 mm	Stal (~0.2)	0.49 kg / 490.0 g 4.8 N
15 mm	Stal (~0.2)	0.17 kg / 172.0 g 1.7 N
20 mm	Stal (~0.2)	0.07 kg / 68.0 g 0.7 N
30 mm	Stal (~0.2)	0.01 kg / 14.0 g 0.1 N
50 mm	Stal (~0.2)	0.00 kg / 2.0 g 0.0 N

The table below presents the estimated holding capacity needed to initiate the slippage of the magnet vertically against a vertical steel wall (considering standard friction coefficient). The holding force depends on the gap size between the magnet and the metal.

Table 3: Vertical assembly (shearing) - behavior on slippery surfaces
MP 25x8x20 / N38

Surface type	Friction coefficient / % Mocy	Max load (kg)
Raw steel	µ = 0.3 30% Nominalnej Siły	5.71 kg / 5706.0 g 56.0 N
Painted steel (standard)	µ = 0.2 20% Nominalnej Siły	3.80 kg / 3804.0 g 37.3 N
Oily/slippery steel	µ = 0.1 10% Nominalnej Siły	1.90 kg / 1902.0 g 18.7 N
Magnet with anti-slip rubber	µ = 0.5 50% Nominalnej Siły	9.51 kg / 9510.0 g 93.3 N

When mounting a magnet on a vertical plane (e.g., a car body), it will only hold only approx. 1/5 of its maximum pull force. Gravity as well as a weak degree of grip mean that products move down faster than they pop off the substrate. Planning a wall mount? Note that the sliding force is significantly lower than the perpendicular breakaway force. On a painted metal, the holder will slide down under a significantly smaller load. Utilizing a rubberized layer can drastically raise the stability.

Table 4: Steel thickness (substrate influence) - sheet metal selection
MP 25x8x20 / N38

Steel thickness (mm)	% power	Real pull force (kg)
0.5 mm	5%	0.95 kg / 951.0 g 9.3 N
1 mm	13%	2.38 kg / 2377.5 g 23.3 N
2 mm	25%	4.76 kg / 4755.0 g 46.6 N
5 mm	63%	11.89 kg / 11887.5 g 116.6 N
10 mm	100%	19.02 kg / 19020.0 g 186.6 N

A too thin steel is incapable of absorb the entire magnetic field, which wastes potential of the magnet. If you mount a strong magnet to a thin surface, the field will pass right through and the pull force will drop sharply. To squeeze full efficiency of this magnet's potential, you need a suitably thick element of metal. The material oversaturation causes that on sheet metal structures (e.g., car bodies), the product shows lower pull force. We advise picking the steel cross-section from these parameters.

Table 5: Thermal resistance (material behavior) - thermal limit
MP 25x8x20 / N38

Ambient temp. (°C)	Power loss	Remaining pull	Status
20 °C	0.0%	19.02 kg / 19020.0 g 186.6 N	OK
40 °C	-2.2%	18.60 kg / 18601.6 g 182.5 N	OK
60 °C	-4.4%	18.18 kg / 18183.1 g 178.4 N	OK
80 °C	-6.6%	17.76 kg / 17764.7 g 174.3 N
100 °C	-28.8%	13.54 kg / 13542.2 g 132.8 N

Ordinary NdFeB products lose power after exceeding the maximum temperature. Watch out for overheating – excessive heat can irreversibly damage this magnet. As the temperature rises, the magnet's power momentarily lowers. Avoid using this product near heat sources higher than its working range. Ignoring the limit will lead to destruction of magnetic properties.

*Engineering 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. The danger warning in the table signals permanent field degradation for this particular item.

Table 6: Two magnets (attraction) - field collision
MP 25x8x20 / N38

Gap (mm)	Attraction (kg) (N-S)	Repulsion (kg) (N-N)
0 mm	30.91 kg / 30909 g 303.2 N 6 082 Gs	N/A
1 mm	28.48 kg / 28480 g 279.4 N 11 091 Gs	25.63 kg / 25632 g 251.5 N ~0 Gs
2 mm	26.11 kg / 26112 g 256.2 N 10 620 Gs	23.50 kg / 23500 g 230.5 N ~0 Gs
3 mm	23.86 kg / 23863 g 234.1 N 10 153 Gs	21.48 kg / 21477 g 210.7 N ~0 Gs
5 mm	19.76 kg / 19758 g 193.8 N 9 238 Gs	17.78 kg / 17782 g 174.4 N ~0 Gs
10 mm	11.84 kg / 11842 g 116.2 N 7 152 Gs	10.66 kg / 10658 g 104.6 N ~0 Gs
20 mm	3.98 kg / 3978 g 39.0 N 4 145 Gs	3.58 kg / 3581 g 35.1 N ~0 Gs
50 mm	0.24 kg / 243 g 2.4 N 1 024 Gs	0.22 kg / 219 g 2.1 N ~0 Gs

Two magnets interact from a significantly greater distance than a magnet and steel combination. The setup of two magnets produces a massive flux and a further horizon of performance. Planning to create a solid fastener? Use a pair of magnets instead of one magnet and a steel. Remember that when connecting a pair of magnets, the collision energy is huge. The levitation is slightly lower than the attraction, but still large.
*Flux density in repulsion mode is approximately ~0 Gs in the exact middle between the magnets (resulting from vector opposition).

Table 7: Protective zones (implants) - precautionary measures
MP 25x8x20 / N38

Object / Device	Limit (Gauss) / mT	Safe distance
Pacemaker	5 Gs (0.5 mT)	17.0 cm
Hearing aid	10 Gs (1.0 mT)	13.5 cm
Timepiece	20 Gs (2.0 mT)	10.5 cm
Phone / Smartphone	40 Gs (4.0 mT)	8.0 cm
Car key	50 Gs (5.0 mT)	7.5 cm
Payment card	400 Gs (40.0 mT)	3.0 cm
HDD hard drive	600 Gs (60.0 mT)	2.5 cm

A strong magnetic field poses a real danger to electronics as well as medical implants. These NdFeB products produce a flux that destroys function of sensitive medical devices. Notice: the invisible magnetic field passes through tissues and housings. Increased vigilance must be taken by people with cochlear implants and insulin pumps. Also at risk are: automatic timepieces, car keys, speakers, and screens. Do not bring the product near payment cards, HDD media, or precise measuring instruments.

Table 8: Impact energy (kinetic energy) - collision effects
MP 25x8x20 / N38

Start from (mm)	Speed (km/h)	Energy (J)
10 mm	18.43 km/h (5.12 m/s)	0.87 J
30 mm	29.70 km/h (8.25 m/s)	2.25 J
50 mm	38.27 km/h (10.63 m/s)	3.73 J
100 mm	54.10 km/h (15.03 m/s)	7.46 J

NdFeB products are very brittle – a strong collision with metal can result in shattering. Watch the impact speed – a magnet released freely turns into a projectile. Impact energy can cause material chips or injury to fingers. Be sure to control the product during installation so it doesn't hit with great force against the metal. A collision at high speed almost guarantees destruction of the magnet. Wear safety glasses when playing with large magnets.

Table 9: Coating parameters (durability)
MP 25x8x20 / 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)

Neodymium magnets are highly susceptible to corrosion without proper protection. The silver nickel coating also serves an aesthetic function but is not fully waterproof.

Table 10: Electrical data (Flux)
MP 25x8x20 / N38

Parameter	Value	SI Unit / Description
Magnetic Flux	10 108 Mx	101.1 µWb
P_c Coefficient	1.25	High (Stable)

Flux value passing through the magnet pole. Key data for generator designers and motors. The P_c coefficient determines the magnet's operating point.

Table 11: Submerged application
MP 25x8x20 / N38

Environment	Effective steel pull	Effect
Air (land)	19.02 kg	Standard
Water (riverbed)	21.78 kg (+2.76 kg Buoyancy gain)	+14.5%

Corrosion warning: Standard nickel requires drying after every contact with moisture; lack of maintenance will lead to rust spots.

In water, the magnet feels stronger thanks to Archimedes' principle. However, remember the water resistance when pulling the rope quickly.

1. Shear force

*Warning: On a vertical wall, the magnet retains merely a fraction of its max power.

2. Steel saturation

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

3. Heat tolerance

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

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

chart generated for the permeance coefficient P_c (Permeance Coefficient) = 1.25

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 P_c (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 P_c 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%

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: 030450-2025

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It is ideally suited for places where solid attachment of the magnet to the substrate is required without the risk of detachment. Thanks to the hole (often for a screw), this model enables quick installation to wood, wall, plastic, or metal. 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 too much pressure 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. This product is dedicated for indoor use. For outdoor applications, we recommend choosing rubberized holders or additional protection with varnish.

A screw or bolt with a thread diameter smaller than 8 mm fits this model. For magnets with a straight hole, a conical head can act like a wedge and burst the magnet. Always check that the screw head is not larger than the outer diameter of the magnet (25 mm), so it doesn't protrude beyond the outline.

This model is characterized by dimensions Ø25x20 mm and a weight of 66.09 g. The key parameter here is the holding force amounting to approximately 19.02 kg (force ~186.54 N). The product has a [NiCuNi] coating and is made of NdFeB material. Inner hole dimension: 8 mm.

These magnets are magnetized axially (through the thickness), which means one flat side is the N pole and the other is S. 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.

Pros and cons of rare earth magnets.

Strengths

Apart from their strong magnetism, neodymium magnets have these key benefits:

Their power is durable, and after approximately ten years it drops only by ~1% (according to research),
They do not lose their magnetic properties even under close interference source,
The use of an elegant layer of noble metals (nickel, gold, silver) causes the element to present itself better,
Magnetic induction on the top side of the magnet remains strong,
Due to their durability and thermal resistance, neodymium magnets can operate (depending on the shape) even at high temperatures reaching 230°C or more...
Due to the potential of precise molding and customization to individualized projects, NdFeB magnets can be modeled in a broad palette of shapes and sizes, which expands the range of possible applications,
Fundamental importance in advanced technology sectors – they serve a role in mass storage devices, drive modules, advanced medical instruments, and multitasking production systems.
Thanks to their power density, small magnets offer high operating force, with minimal size,

Limitations

Disadvantages of neodymium magnets:

Brittleness is one of their disadvantages. Upon intense impact they can fracture. We advise keeping them in a strong case, which not only protects them against impacts but also increases their durability
We warn that neodymium magnets can lose their strength at high temperatures. To prevent this, we suggest our specialized [AH] magnets, which work effectively even at 230°C.
Magnets exposed to a humid environment can corrode. Therefore while using outdoors, we suggest using water-impermeable magnets made of rubber, plastic or other material protecting against moisture
Limited ability of creating threads in the magnet and complex forms - preferred is cover - magnetic holder.
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. Furthermore, tiny parts of these magnets are able to be problematic in diagnostics medical after entering the body.
With mass production the cost of neodymium magnets can be a barrier,

Holding force characteristics

Maximum magnetic pulling force – what affects it?

The load parameter shown represents the limit force, measured under laboratory conditions, specifically:

using a base made of high-permeability steel, serving as a magnetic yoke
possessing a massiveness of at least 10 mm to avoid saturation
characterized by even structure
without any insulating layer between the magnet and steel
during pulling in a direction vertical to the plane
at conditions approx. 20°C

Magnet lifting force in use – key factors

Real force impacted by working environment parameters, such as (from most important):

Gap between surfaces – every millimeter of distance (caused e.g. by varnish or unevenness) drastically reduces the magnet efficiency, often by half at just 0.5 mm.
Loading method – declared lifting capacity refers to pulling vertically. When slipping, the magnet exhibits much less (often approx. 20-30% of nominal force).
Metal thickness – thin material does not allow full use of the magnet. Magnetic flux passes through the material instead of generating force.
Chemical composition of the base – mild steel gives the best results. Alloy admixtures decrease magnetic permeability and holding force.
Base smoothness – the more even the surface, the better the adhesion and higher the lifting capacity. Roughness creates an air distance.
Temperature influence – hot environment reduces magnetic field. Exceeding the limit temperature can permanently demagnetize the magnet.

Holding force was checked on a smooth steel plate of 20 mm thickness, when a perpendicular force was applied, whereas under parallel forces the load capacity is reduced by as much as 5 times. Moreover, even a minimal clearance between the magnet and the plate lowers the holding force.

Warnings

Allergy Warning

A percentage of the population have a hypersensitivity to Ni, which is the common plating for neodymium magnets. Extended handling may cause an allergic reaction. We recommend wear protective gloves.

Danger to the youngest

NdFeB magnets are not toys. Swallowing several magnets can lead to them pinching intestinal walls, which constitutes a critical condition and requires immediate surgery.

GPS Danger

Navigation devices and smartphones are extremely susceptible to magnetism. Direct contact with a powerful NdFeB magnet can permanently damage the sensors in your phone.

Dust is flammable

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

Permanent damage

Standard neodymium magnets (grade N) lose magnetization when the temperature surpasses 80°C. Damage is permanent.

Safe operation

Before starting, check safety instructions. Sudden snapping can break the magnet or hurt your hand. Be predictive.

Crushing force

Risk of injury: The attraction force is so immense that it can cause blood blisters, crushing, and even bone fractures. Protective gloves are recommended.

Protective goggles

NdFeB magnets are ceramic materials, meaning they are prone to chipping. Impact of two magnets will cause them breaking into shards.

Cards and drives

Data protection: Strong magnets can ruin payment cards and delicate electronics (pacemakers, hearing aids, mechanical watches).

Medical implants

People with a ICD should keep an absolute distance from magnets. The magnetism can stop the operation of the implant.

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

MP 25x8x20 / N38 - ring magnet

Need advice?

MP 25x8x20 / N38 - ring magnet

Magnetic properties of material N38

Physical properties of sintered neodymium magnets Nd2Fe14B at 20°C

Physical modeling of the product - report

1. Shear force

2. Steel saturation

3. Heat tolerance

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

Elemental analysis

Sustainability

Magnet pull force

Field Strength

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Pros and cons of rare earth magnets.

Strengths

Limitations

Holding force characteristics

Maximum magnetic pulling force – what affects it?

Magnet lifting force in use – key factors

Allergy Warning

Danger to the youngest

GPS Danger

Dust is flammable

Permanent damage

Safe operation

Crushing force

Protective goggles

Cards and drives

Medical implants

Physical properties of sintered neodymium magnets Nd₂Fe₁₄B at 20°C