Why Your Round Magnet Keeps Failing — And How to Pick the Right One

Round Magnets are among the most widely used magnetic components in industrial automation, machinery, jigs, fixtures, and precision equipment. Their compact circular design, reliable holding force, and ease of installation make them ideal for positioning, fixing, sensing, and holding applications across manufacturing industries. Whether used to secure machine covers, locate workpieces, or mount sensors, round magnets provide a simple yet highly effective solution for improving operational efficiency and equipment reliability.

At MISUMI, engineers can choose from a broad range of round magnets designed for diverse industrial requirements. The selection includes Alnico, Neodymium, and Cobalt magnet types with different mounting configurations such as plain cylindrical, countersunk, and tapped designs.

Round magnets are cylindrical permanent magnets that generate a stable magnetic field without any external power supply. They are manufactured in a range of diameters — typically 8 mm to 25 mm for industrial automation components — and are available in plain cylindrical, countersunk, and tapped configurations to suit diverse installation requirements.

Key Physical Characteristics

• Compact cylindrical or flat disc form factor
• High surface magnetic flux densities (approximately 1,100 to 4,400 Gauss depending on material and size)
• Attraction forces ranging from 3.9 N to over 114.7 N for a single magnet element
• Corrosion-resistant surface treatments such as electroless nickel plating
• Mounting options: plain, countersunk, or tapped holes for screw fastening

1. MG Series — Alnico Magnets (General Purpose)

• Magnet Material: Alnico (Aluminium-Nickel-Cobalt alloy)
• Heat Resistance: Up to 80°C
• Structural Materials: SUM24L steel and Brass (C3604BD)

2. MGN Series — Neodymium Magnets (Strong Corrosion-Resistant Type)

• Magnet Material: Neodymium (NdFeB)
• Heat Resistance: Up to 80°C
• Surface Treatment: Electroless nickel plating
• Structural Material: SUM24L steel

3. HX / HXH / HXU Series — Cobalt Magnets (Standard High-Temperature)

• Magnet Material: Samarium-Cobalt (SmCo)
• Heat Resistance: Up to 80°C (HX/HXH/HXU)
• Structural Materials: SUM24L and Brass (C3604BD)

4. HXMB Series — Cobalt Magnets (High-Temperature, 200°C)

• Magnet Material: Samarium-Cobalt (SmCo)
• Heat Resistance: Up to 200°C

The table below summarizes reference attraction force and surface magnetic flux density values for representative MISUMI round magnet sizes. Values are for the magnet element itself; actual holding force in an assembled fixture will vary based on the target material, air gap, and mounting configuration.

Diameter	Series	Magnet Material	Attraction Force (N)	Surface Flux Density (G)
Ø8 mm	MG / MGN / HX	Alnico / NdFeB / SmCo	~3.9 N {0.4 kgf}	~1,200 – 3,900 G
Ø12 mm	MG / MGN / HX	Alnico / NdFeB / SmCo	~15.7 – 68.6 N	~3,200 – 4,000 G
Ø20 mm	MGN / HXMB	NdFeB / SmCo (200°C)	Up to ~114.7 N {11.7 kgf}	~4,000 – 4,400 G
Ø25 mm	MG / HX variants	Alnico / SmCo	Refer to MISUMI catalogue	Refer to MISUMI catalogue

Selecting the correct round magnet is not solely about choosing the strongest available option. The following decision framework helps engineers and buyers arrive at the most suitable series and size:

1. Operating Temperature

This is the most critical filter. Map your operating environment:

• Up to 80°C ambient: MG (Alnico), MGN (Neodymium), HX/HXH/HXU (Cobalt) series are all applicable.
• Up to 200°C ambient or near heat sources: HXMB (Cobalt) series is mandatory — do not use MGN in high-temperature environments as Neodymium magnets can suffer irreversible demagnetisation above approximately 80–150°C depending on grade.

2. Required Holding Force

Calculate the minimum holding force required by your application, applying a safety factor of at least 2x–3x the expected load. Reference attraction force values are measured on a flat steel surface with no air gap; real-world forces will be lower depending on surface finish, gap, and contact geometry. A Ø8 mm magnet provides approximately 3.9 N, while a Ø20 mm MGN magnet can reach 114.7 N — a 29x difference for a 2.5x increase in diameter.

3. Corrosion and Environmental Resistance

For humid environments, wash-down zones, or applications with light chemical exposure:

• MGN (Neodymium with electroless nickel plating): Excellent corrosion resistance for standard humidity and light chemical exposure.
• HX/HXH/HXU/HXMB (Cobalt series): Inherently corrosion-resistant cobalt composition, suitable for demanding environments without additional surface treatment.
• MG (Alnico, SUM24L body): Suitable for dry indoor environments; verify corrosion requirements before selecting.

4. Mounting Configuration

MISUMI round magnets are available in three mounting configurations:

• Plain cylindrical: Press-fit or adhesive into a blind bore — the simplest installation.
• Countersunk: Allows flush mounting with a countersunk screw through the magnet body into the host fixture.
• Tapped: Permits mounting via a machine screw threaded directly into the magnet assembly — common in removable panels and adjustable jig elements.

5. Mechanical Handling

Important: All permanent magnets in this range are brittle ceramic or alloy components. Mechanical machining, drilling, or modification of the magnet itself is strictly not permitted and will cause cracking or fracture. End face grinding may be applied by MISUMI on certain types. Engineers must also take care during installation: if two magnets or a magnet and a ferrous surface are allowed to attract at speed, the impact can crack the magnet. Use gradual, controlled approaches during assembly.

Choosing the correct magnet material directly impacts equipment performance.

Magnet Material	Primary Advantage	Typical Applications
Alnico	Stable magnetic performance	General industrial equipment
Neodymium	Highest holding force	Compact fixtures, automation systems
Cobalt	Better temperature stability	Precision machinery
High-temperature Cobalt	Excellent heat resistance	High-temperature industrial equipment

Based on MISUMI's technical documentation and industry best practices, the following guidance helps ensure correct specification and safe use of round magnets:

• Always apply a safety factor: Published attraction force values are reference figures measured under ideal conditions (flat, clean steel, zero air gap). Real-world assembly forces are typically 30–60% lower. Design to at least 2x–3x the expected load.
• Avoid demagnetisation: Keep magnets away from strong alternating magnetic fields and do not operate above the rated temperature. For HXMB series, verify that peak transient temperatures in the application do not exceed 200°C.
• Account for brittleness: Permanent magnets crack under impact or bending stress. Design fixtures so the magnet is loaded in compression (held in a bore), not in tension or shear, wherever possible.
• Verify surface treatment for your environment: The MGN series electroless nickel plating provides excellent moisture resistance; for aggressive chemical environments, consult MISUMI's technical team.
• Download free CAD data: MISUMI India provides free CAD downloads for all configurable magnet products, enabling engineers to integrate accurate magnet geometry into their 3D assembly models without manual modelling effort.
• No minimum order: MISUMI India offers round magnets with no minimum order quantity, making prototyping, trial batches, and single-unit replacement straightforward.