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MP 25x7.5/4.5x5 / 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 030194

GTIN/EAN: 5906301812111

5.00

Diameter

25 mm [±0,1 mm]

internal diameter Ø

7.5/4.5 mm [±0,1 mm]

Height

5 mm [±0,1 mm]

Weight

17.81 g

Magnetization Direction

↑ axial

Load capacity

7.72 kg / 75.69 N

Magnetic Induction

230.20 mT / 2302 Gs

Coating

[NiCuNi] Nickel

8.00 ZŁ with VAT / pcs + price for transport

6.50 ZŁ net + 23% VAT / pcs

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MP 25x7.5/4.5x5 / N38 - ring magnet

Specification / characteristics MP 25x7.5/4.5x5 / N38 - ring magnet

properties

properties	values
Cat. no.	030194
GTIN/EAN	5906301812111
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	7.5/4.5 mm [±0,1 mm]
Height	5 mm [±0,1 mm]
Weight	17.81 g
Magnetization Direction	↑ axial
Load capacity ~ ?	7.72 kg / 75.69 N
Magnetic Induction ~ ?	230.20 mT / 2302 Gs
Coating	[NiCuNi] Nickel
Manufacturing Tolerance	±0.1 mm

Magnetic properties of material N38

Specification / characteristics MP 25x7.5/4.5x5 / 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

Technical modeling of the magnet - report

Presented values are the result of a engineering analysis. Values were calculated on algorithms for the material Nd₂Fe₁₄B. Operational performance might slightly differ from theoretical values. Use these data as a reference point during assembly planning.

Table 1: Static force (pull vs gap) - characteristics
MP 25x7.5/4.5x5 / N38

Distance (mm)	Induction (Gauss) / mT	Pull Force (kg)	Risk Status
0 mm	1995 Gs 199.5 mT	7.72 kg / 7720.0 g 75.7 N	warning
1 mm	1906 Gs 190.6 mT	7.05 kg / 7049.4 g 69.2 N	warning
2 mm	1793 Gs 179.3 mT	6.24 kg / 6236.8 g 61.2 N	warning
3 mm	1664 Gs 166.4 mT	5.37 kg / 5368.9 g 52.7 N	warning
5 mm	1385 Gs 138.5 mT	3.72 kg / 3722.8 g 36.5 N	warning
10 mm	788 Gs 78.8 mT	1.20 kg / 1203.8 g 11.8 N	weak grip
15 mm	437 Gs 43.7 mT	0.37 kg / 370.3 g 3.6 N	weak grip
20 mm	253 Gs 25.3 mT	0.12 kg / 124.5 g 1.2 N	weak grip
30 mm	101 Gs 10.1 mT	0.02 kg / 19.8 g 0.2 N	weak grip
50 mm	27 Gs 2.7 mT	0.00 kg / 1.4 g 0.0 N	weak grip

Magnetic force drops sharply with every mm of distance. Note that even a microscopic distance (e.g., dirt, varnish, veneer) significantly diminishes the holding power. Neodymiums hold most effectively during direct contact; air break weakens the power. Notice how rapidly the parameters plummet, when the product does not touch flatly to the steel surface. When planning the assembly, avoid unnecessary gaps.

Table 2: Slippage hold (wall)
MP 25x7.5/4.5x5 / N38

Distance (mm)	Friction coefficient	Pull Force (kg)
0 mm	Stal (~0.2)	1.54 kg / 1544.0 g 15.1 N
1 mm	Stal (~0.2)	1.41 kg / 1410.0 g 13.8 N
2 mm	Stal (~0.2)	1.25 kg / 1248.0 g 12.2 N
3 mm	Stal (~0.2)	1.07 kg / 1074.0 g 10.5 N
5 mm	Stal (~0.2)	0.74 kg / 744.0 g 7.3 N
10 mm	Stal (~0.2)	0.24 kg / 240.0 g 2.4 N
15 mm	Stal (~0.2)	0.07 kg / 74.0 g 0.7 N
20 mm	Stal (~0.2)	0.02 kg / 24.0 g 0.2 N
30 mm	Stal (~0.2)	0.00 kg / 4.0 g 0.0 N
50 mm	Stal (~0.2)	0.00 kg / 0.0 g 0.0 N

The following data defines the estimated force required to initiate the slippage of the magnet downwards along a vertical steel plate (considering typical friction coefficient). The holding force is a function of the distance between the magnet and the metal.

Table 3: Vertical assembly (sliding) - vertical pull
MP 25x7.5/4.5x5 / N38

Surface type	Friction coefficient / % Mocy	Max load (kg)
Raw steel	µ = 0.3 30% Nominalnej Siły	2.32 kg / 2316.0 g 22.7 N
Painted steel (standard)	µ = 0.2 20% Nominalnej Siły	1.54 kg / 1544.0 g 15.1 N
Oily/slippery steel	µ = 0.1 10% Nominalnej Siły	0.77 kg / 772.0 g 7.6 N
Magnet with anti-slip rubber	µ = 0.5 50% Nominalnej Siły	3.86 kg / 3860.0 g 37.9 N

When hanging a holder on a upright plane (e.g., a car body), it you can count on only about 20%-30% of nominal attraction strength. Gravitational force as well as a low friction coefficient cause that magnets slip easier than they detach. Want to create a hanger? Note that the sliding force is much weaker than the maximum static pull force. On a painted metal, the element will slide down under a much lighter cargo. Application of an anti-slip coating can effectively improve the result.

Table 4: Steel thickness (substrate influence) - power losses
MP 25x7.5/4.5x5 / N38

Steel thickness (mm)	% power	Real pull force (kg)
0.5 mm	10%	0.77 kg / 772.0 g 7.6 N
1 mm	25%	1.93 kg / 1930.0 g 18.9 N
2 mm	50%	3.86 kg / 3860.0 g 37.9 N
5 mm	100%	7.72 kg / 7720.0 g 75.7 N
10 mm	100%	7.72 kg / 7720.0 g 75.7 N

A too thin steel is not enough to absorb the entire magnetic field, which weakens actual performance of the holder. If you attach a powerful product to a thin surface, the flux will pass right through and the attraction force will be weaker. To achieve 100% of this neodymium's power, you need a suitably thick element of metal. The saturation effect means that on sheet metal structures (e.g., thin profiles), the magnet shows lower pull force. We advise picking the steel dimension according to the table below.

Table 5: Thermal stability (material behavior) - power drop
MP 25x7.5/4.5x5 / N38

Ambient temp. (°C)	Power loss	Remaining pull	Status
20 °C	0.0%	7.72 kg / 7720.0 g 75.7 N	OK
40 °C	-2.2%	7.55 kg / 7550.2 g 74.1 N	OK
60 °C	-4.4%	7.38 kg / 7380.3 g 72.4 N
80 °C	-6.6%	7.21 kg / 7210.5 g 70.7 N
100 °C	-28.8%	5.50 kg / 5496.6 g 53.9 N

Standard neodymium magnets change their properties parameters after exceeding the maximum temperature. Watch out for overheating – high temperature can permanently destroy this magnet. With increasing heat, the magnet's power briefly lowers. Refrain from using this magnet near heat sources exceeding its operating temperature limit. Too high temperature will result in irreversible degradation of magnetic properties.

*Engineering note: Temperature resistance is determined by both grade, but also on the magnet's shape. Low-profile magnets (pancake types) are more susceptible to demagnetization at lower temperatures than taller cylinders. Warning indicator in the table indicates a risk of irreversible loss for this particular item.

Table 6: Two magnets (attraction) - field range
MP 25x7.5/4.5x5 / N38

Gap (mm)	Attraction (kg) (N-S)	Repulsion (kg) (N-N)
0 mm	9.91 kg / 9907 g 97.2 N 3 484 Gs	N/A
1 mm	9.51 kg / 9509 g 93.3 N 3 909 Gs	8.56 kg / 8558 g 84.0 N ~0 Gs
2 mm	9.05 kg / 9046 g 88.7 N 3 813 Gs	8.14 kg / 8141 g 79.9 N ~0 Gs
3 mm	8.54 kg / 8540 g 83.8 N 3 705 Gs	7.69 kg / 7686 g 75.4 N ~0 Gs
5 mm	7.45 kg / 7449 g 73.1 N 3 460 Gs	6.70 kg / 6704 g 65.8 N ~0 Gs
10 mm	4.78 kg / 4777 g 46.9 N 2 771 Gs	4.30 kg / 4299 g 42.2 N ~0 Gs
20 mm	1.54 kg / 1545 g 15.2 N 1 576 Gs	1.39 kg / 1390 g 13.6 N ~0 Gs
50 mm	0.06 kg / 60 g 0.6 N 312 Gs	0.05 kg / 54 g 0.5 N ~0 Gs

Two strong neodymiums attract each other from a wider radius than a magnet and steel setup. Such a system of two magnets generates a stronger field and a further horizon of action. Designing a solid fastener? Apply two magnets instead of a neodymium and a steel. Be careful that when connecting a pair of magnets, the collision energy is extreme. The levitation is a bit weaker than the attraction, but still large.
*The magnetic induction for N-N configuration reaches ~0 Gs in the exact middle between the magnets (caused by magnetic field nullification).

Table 7: Hazards (electronics) - warnings
MP 25x7.5/4.5x5 / N38

Object / Device	Limit (Gauss) / mT	Safe distance
Pacemaker	5 Gs (0.5 mT)	9.5 cm
Hearing aid	10 Gs (1.0 mT)	7.5 cm
Mechanical watch	20 Gs (2.0 mT)	6.0 cm
Phone / Smartphone	40 Gs (4.0 mT)	4.5 cm
Car key	50 Gs (5.0 mT)	4.0 cm
Payment card	400 Gs (40.0 mT)	2.0 cm
HDD hard drive	600 Gs (60.0 mT)	1.5 cm

Powerful magnet radiation is a large risk to electronics and pacemakers. These neodymiums generate a field that prevents correct functioning of digital equipment. Remember: the unseen radiation acts through matter and housings. Exceptional care must be exercised by people with hearing aids and drug dispensers. Influence will be felt by: automatic timepieces, remotes, speakers, and screens. Avoid contact with magnetic cards, HDD media, or sensitive navigation tools.

Table 8: Collisions (cracking risk) - warning
MP 25x7.5/4.5x5 / N38

Start from (mm)	Speed (km/h)	Energy (J)
10 mm	22.95 km/h (6.38 m/s)	0.36 J
30 mm	36.43 km/h (10.12 m/s)	0.91 J
50 mm	46.96 km/h (13.04 m/s)	1.52 J
100 mm	66.40 km/h (18.44 m/s)	3.03 J

Magnetic elements are delicate – a violent impact against metal risks their cracking. Pay attention to connection velocity – a neodymium left loose speeds with massive force. Impact energy can trigger coating fragments or dangerous crushing to fingers. Be sure to control the product during mounting so it doesn't hit with great force against the metal. A collision at high speed ends with a crack of the neodymium. Wear safety glasses when working with large magnets.

Table 9: Coating parameters (durability)
MP 25x7.5/4.5x5 / 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)

The following table defines the conditions under which this product can be safely used. Moisture resistance is crucial for installations in bathrooms or outdoors.

Table 10: Construction data (Flux)
MP 25x7.5/4.5x5 / N38

Parameter	Value	SI Unit / Description
Magnetic Flux	9 759 Mx	97.6 µWb
P_c Coefficient	0.25	Low (Flat)

Flux value passing through the pole surface. Essential parameter when building generators and motors. P_c value defines the working geometry.

Table 11: Underwater work (magnet fishing)
MP 25x7.5/4.5x5 / N38

Environment	Effective steel pull	Effect
Air (land)	7.72 kg	Standard
Water (riverbed)	8.84 kg (+1.12 kg Buoyancy gain)	+14.5%

Rust risk: 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. Vertical hold

*Note: On a vertical surface, the magnet retains merely ~20% 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 N38 grade, the max working temp is 80°C.

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

chart generated for the permeance coefficient P_c (Permeance Coefficient) = 0.25

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.

Technical specification and ecology

Material specification

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: 030194-2025

Measurement Calculator

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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. Mounting is clean and reversible, unlike gluing. It is also often used in advertising for fixing signs and in workshops for organizing tools.

This is a crucial issue when working with model MP 25x7.5/4.5x5 / N38. Neodymium magnets are sintered ceramics, which means they are very brittle and inelastic. 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. If you must use it outside, paint it with anti-corrosion paint after mounting.

A screw or bolt with a thread diameter smaller than 7.5/4.5 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.

The presented product is a ring magnet with dimensions Ø25 mm (outer diameter) and height 5 mm. The key parameter here is the lifting capacity amounting to approximately 7.72 kg (force ~75.69 N). The mounting hole diameter is precisely 7.5/4.5 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. When ordering a larger quantity, magnets are usually packed in stacks, where they are already naturally paired.

Strengths as well as weaknesses of Nd₂Fe₁₄B magnets.

Benefits

Besides their high retention, neodymium magnets are valued for these benefits:

They do not lose magnetism, even over nearly 10 years – the drop in power is only ~1% (theoretically),
They retain their magnetic properties even under external field action,
By using a decorative layer of silver, the element acquires an professional look,
The surface of neodymium magnets generates a intense magnetic field – this is a key feature,
Through (adequate) combination of ingredients, they can achieve high thermal resistance, allowing for functioning at temperatures approaching 230°C and above...
Possibility of detailed shaping as well as adjusting to individual needs,
Universal use in future technologies – they are used in magnetic memories, motor assemblies, diagnostic systems, also multitasking production systems.
Thanks to concentrated force, small magnets offer high operating force, with minimal size,

Weaknesses

Drawbacks and weaknesses of neodymium magnets: tips and applications.

At very strong impacts they can break, therefore we recommend placing them in steel cases. A metal housing provides additional protection against damage, as well as increases the magnet's durability.
NdFeB magnets lose power when exposed to high temperatures. After reaching 80°C, many of them experience permanent weakening of power (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 usually rust. To use them in conditions outside, it is recommended to use protective magnets, such as those in rubber or plastics, which secure oxidation and corrosion.
Due to limitations in realizing threads and complicated forms in magnets, we propose using cover - magnetic mount.
Possible danger related to microscopic parts of magnets are risky, in case of ingestion, which gains importance in the context of child safety. Furthermore, tiny parts of these magnets are able to complicate diagnosis medical when they are in the body.
Higher cost of purchase is one of the disadvantages compared to ceramic magnets, especially in budget applications

Pull force analysis

Maximum magnetic pulling force – what it depends on?

Magnet power was defined for ideal contact conditions, taking into account:

using a base made of mild steel, acting as a magnetic yoke
possessing a thickness of at least 10 mm to avoid saturation
with a surface free of scratches
under conditions of gap-free contact (surface-to-surface)
under axial application of breakaway force (90-degree angle)
at ambient temperature room level

Determinants of lifting force in real conditions

Holding efficiency is influenced by working environment parameters, such as (from most important):

Gap between surfaces – even a fraction of a millimeter of distance (caused e.g. by veneer or unevenness) diminishes the magnet efficiency, often by half at just 0.5 mm.
Angle of force application – highest force is available only during pulling at a 90° angle. The resistance to sliding of the magnet along the surface is standardly many times smaller (approx. 1/5 of the lifting capacity).
Wall thickness – thin material does not allow full use of the magnet. Magnetic flux penetrates through instead of generating force.
Plate material – mild steel attracts best. Higher carbon content lower magnetic permeability and lifting capacity.
Smoothness – full contact is obtained only on smooth steel. Rough texture create air cushions, reducing force.
Operating temperature – neodymium magnets have a negative temperature coefficient. At higher temperatures they lose power, and in frost they can be stronger (up to a certain limit).

Lifting capacity testing was carried out on a smooth plate of optimal thickness, under a perpendicular pulling force, however under parallel forces the load capacity is reduced by as much as 75%. Moreover, even a minimal clearance between the magnet’s surface and the plate lowers the load capacity.

Warnings

Safe operation

Be careful. Rare earth magnets attract from a distance and connect with huge force, often quicker than you can react.

Crushing risk

Big blocks can break fingers in a fraction of a second. Under no circumstances place your hand betwixt two strong magnets.

Heat warning

Monitor thermal conditions. Heating the magnet to high heat will destroy its properties and pulling force.

Do not give to children

Product intended for adults. Tiny parts pose a choking risk, causing severe trauma. Store away from children and animals.

Allergy Warning

Certain individuals experience a sensitization to nickel, which is the common plating for neodymium magnets. Frequent touching can result in dermatitis. We recommend wear protective gloves.

Impact on smartphones

Be aware: rare earth magnets produce a field that interferes with sensitive sensors. Keep a separation from your phone, device, and GPS.

Medical implants

Patients with a ICD have to keep an absolute distance from magnets. The magnetic field can stop the operation of the life-saving device.

Dust explosion hazard

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

Risk of cracking

NdFeB magnets are sintered ceramics, meaning they are very brittle. Collision of two magnets leads to them breaking into small pieces.

Cards and drives

Avoid bringing magnets close to a wallet, laptop, or screen. The magnetism can destroy these devices and wipe information from cards.

Security! Details about hazards in the article: Safety of working with magnets.

MP 25x7.5/4.5x5 / N38 - ring magnet

Want to negotiate?

MP 25x7.5/4.5x5 / N38 - ring magnet

Magnetic properties of material N38

Physical properties of sintered neodymium magnets Nd2Fe14B at 20°C

Technical modeling of the magnet - report

1. Vertical hold

2. Steel saturation

3. Heat tolerance

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

Material specification

Sustainability

Force (pull)

Magnetic Field

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Strengths as well as weaknesses of Nd2Fe14B magnets.

Benefits

Weaknesses

Pull force analysis

Maximum magnetic pulling force – what it depends on?

Determinants of lifting force in real conditions

Safe operation

Crushing risk

Heat warning

Do not give to children

Allergy Warning

Impact on smartphones

Medical implants

Dust explosion hazard

Risk of cracking

Cards and drives

Physical properties of sintered neodymium magnets Nd₂Fe₁₄B at 20°C

Strengths as well as weaknesses of Nd₂Fe₁₄B magnets.