Neodymium Cylinder Magnet – 4mm x 20mm

The Neodymium Cylinder Magnet – 4mm x 20mm is a slim, high-performance rare earth permanent magnet measuring 4mm in diameter x 20mm long. Manufactured from Neodymium Iron Boron (NdFeB), this narrow cylindrical magnet provides strong magnetic performance relative to its compact diameter and is suitable for precision engineering, sensors, instrumentation, electronics, product assemblies, prototypes and custom OEM applications.

Also known as a neodymium rod magnet, rare earth cylinder magnet, NdFeB cylinder magnet, 4mm rod magnet or cylindrical neodymium magnet, its elongated shape has a length five times its diameter. This geometry is particularly useful for integration into narrow cylindrical recesses, tubes, housings and compact mechanical assemblies.

As a permanent magnet, this 4mm x 20mm neodymium cylinder requires no electricity, batteries or charging to maintain its magnetic field.

Key Features

• 4mm diameter
• 20mm length
• Slim cylindrical / rod-shaped profile
• Length is five times the diameter
• Neodymium Iron Boron (NdFeB)
• High-performance rare earth permanent magnet
• Strong magnetic performance relative to size
• Suitable for narrow cylindrical recesses and housings
• Useful for sensors and instrumentation
• Suitable for precision engineering
• Compact diameter for space-restricted assemblies
• Permanent magnetic operation
• No electricity or batteries required
• Suitable for prototype and OEM applications

Common Applications

• Precision engineering
• Sensors and switches
• Instrumentation
• Electronics
• Product assemblies
• Mechanical equipment
• Positioning systems
• Small fixtures
• Models and prototypes
• Laboratory equipment
• Research and development
• Educational projects
• Custom magnetic assemblies
• OEM manufacturing

4mm Diameter x 20mm Long Neodymium Cylinder

This rare earth cylinder magnet measures:

• Diameter: 4mm
• Length: 20mm

With a length five times its diameter, this magnet has a distinctly long and narrow rod-shaped profile.

The 4mm diameter allows it to be incorporated into compact cylindrical spaces, while the 20mm length can be useful for applications requiring an elongated magnetic component.

Potential installations include:

• Cylindrical recesses
• Tubular housings
• Sensor assemblies
• Instrumentation
• Mechanical components
• Prototype devices
• Custom manufactured products

The dimensions describe the physical size of the magnet and should not be interpreted as a pull-force or holding-capacity rating.

Neodymium Iron Boron Rare Earth Magnet

Neodymium Iron Boron (NdFeB) is one of the strongest commercially available permanent magnetic materials.

Its high magnetic performance relative to volume makes neodymium particularly useful for compact engineering and product applications where available space is limited.

NdFeB cylinder magnets are commonly incorporated into:

• Sensors
• Switches
• Instruments
• Mechanical assemblies
• Electronics
• Fixtures
• Prototypes
• OEM products

The specific NdFeB magnetic grade of this cylinder magnet has not been supplied and should not be assumed.

Slim Rod-Shaped Magnet

The 4mm x 20mm geometry provides a slender cylindrical form factor that differs from a conventional disc magnet.

This can make it useful for:

• Narrow housings
• Tubular components
• Deep cylindrical recesses
• Compact sensor assemblies
• Mechanical positioning systems
• Prototype devices

When integrating the magnet into a mechanical assembly, adequate support should be provided to protect it from excessive sideways or bending forces.

Sensors and Instrumentation

Small neodymium cylinder magnets are commonly incorporated into sensor and instrumentation systems where a permanent magnetic field is required.

Potential applications include:

• Position sensing
• Proximity systems
• Magnetic switches
• Reed switch activation
• Instrumentation
• Detection systems
• Prototype electronics
• Mechanical position indicators

The suitability of this magnet for a specific sensor depends on factors including magnetisation direction, magnetic field strength, operating distance, sensor sensitivity and installation geometry.

These parameters should be confirmed for the intended system rather than inferred from the magnet's dimensions.

Magnetisation Direction

The magnetisation direction of this 4mm x 20mm cylinder magnet has not been supplied.

Cylinder magnets may be magnetised in different directions, and the magnet's shape alone should not be used to determine the location of its north and south poles.

Magnetisation direction can affect:

• Pole location
• Sensor response
• Magnetic holding
• Magnet-to-magnet interaction
• Working orientation
• Magnetic circuit design

Where pole orientation is important, magnetisation direction should be confirmed before installation.

Magnetic Holding and Positioning

This cylinder magnet may also be incorporated into magnetic holding and positioning systems.

Potential uses include:

• Locating components
• Magnetic positioning
• Small mechanical assemblies
• Product closures
• Detachable components
• Prototype mechanisms
• Custom magnetic systems

Actual holding performance depends on the complete magnetic and mechanical design.

Magnetic Performance and Air Gaps

Magnetic performance can be affected by:

• NdFeB magnetic grade
• Magnetisation direction
• Target steel thickness
• Target material
• Contact area
• Surface flatness
• Air gaps
• Paint and coatings
• Magnet orientation
• Load direction
• Magnetic circuit geometry

No specific pull force or Gauss rating has been supplied for this product and these values should not be inferred solely from its 4mm x 20mm dimensions.

Because this magnet has a small 4mm diameter, even relatively small air gaps can have a significant effect on practical magnetic interaction.

Compatible Target Materials

Neodymium magnets attract ferromagnetic iron and compatible steels.

Suitable target materials may include:

• Mild steel
• Iron
• Magnetic steel
• Ferromagnetic fasteners
• Compatible machinery components

They will not effectively attract:

• Aluminium
• Copper
• Brass
• Plastic
• Timber
• Glass

Many stainless steel grades may also provide weak or negligible magnetic attraction and should be tested before use.

Bonding a 4mm x 20mm Cylinder Magnet

The cylindrical shape can make this magnet suitable for bonding into a compatible drilled or moulded recess.

For adhesive installation:

• Clean the magnet and substrate
• Remove grease, dust and contamination
• Select an adhesive suitable for both materials
• Follow the adhesive manufacturer's preparation instructions
• Avoid excessively thick adhesive layers
• Allow the adhesive to cure fully before loading
• Avoid force-fitting the magnet into an undersized hole
• Keep curing temperatures within the magnet's permitted operating conditions

A small clearance for adhesive may be preferable to mechanically forcing the magnet into position.

Protect the Magnet from Bending Forces

Although neodymium magnets are magnetically powerful, NdFeB is mechanically hard and brittle.

The elongated 4mm x 20mm shape should not be treated like a flexible metal rod.

Avoid:

• Bending the magnet
• Using it as a mechanical pin
• Applying strong sideways loads
• Levering against the magnet
• Force-fitting it into a housing
• Striking it against steel
• Allowing it to collide with another magnet

Mechanical support from the surrounding housing may be appropriate in applications where the magnet could otherwise experience sideways loading.

Neodymium vs Ferrite Cylinder Magnets

Neodymium and ferrite are both permanent magnetic materials, but they provide different characteristics.

Neodymium magnets generally offer:

• Much higher magnetic strength relative to size
• Compact dimensions
• Strong performance in space-restricted assemblies
• Suitability for sensors and precision applications

Ferrite magnets are generally:

• More economical
• Naturally corrosion resistant
• Suitable for many general-purpose applications
• Lower in magnetic strength relative to size

Neodymium is often selected when high magnetic performance within a small diameter or compact assembly is important.

Permanent Magnetic Operation

This 4mm x 20mm NdFeB cylinder is a permanent magnet.

It requires:

• No electricity
• No batteries
• No charging
• No electrical wiring

Its magnetic field remains continuously active during normal use.

Technical Specifications

• Product Type: Neodymium Cylinder Magnet
• Alternative Names: Neodymium Rod Magnet, Rare Earth Cylinder Magnet, NdFeB Cylinder Magnet, Cylindrical Neodymium Magnet
• Diameter: 4mm
• Length: 20mm
• Shape: Cylinder / Rod
• Length-to-Diameter Ratio: 5:1
• Magnetic Material: Neodymium Iron Boron (NdFeB)
• Magnet Type: Rare Earth Permanent Magnet
• Magnetic Operation: Permanent
• Power Required: None
• Target Materials: Compatible ferromagnetic iron and steel
• Primary Functions: Sensing, positioning and integration into magnetic assemblies
• Typical Applications: Precision engineering, sensors, instrumentation, electronics, prototypes and OEM products

Precision Engineering and OEM Applications

The combination of a 4mm diameter and 20mm length makes this neodymium cylinder magnet particularly suitable for compact products requiring a long, narrow magnetic component.

Potential users include:

• Engineers
• Product designers
• Electronics manufacturers
• Sensor manufacturers
• Instrumentation companies
• Research laboratories
• Prototype developers
• Equipment manufacturers
• OEM manufacturers

For technical applications, magnetic performance should be evaluated as part of the complete magnetic circuit, sensor system, mechanical assembly and operating environment.

Handling Small Neodymium Cylinder Magnets

Neodymium magnets can produce strong attraction relative to their size and should be handled carefully.

NdFeB is also hard and brittle and can chip, crack or fracture if subjected to impact or excessive mechanical force.

Do not:

• Drill the magnet
• Cut the magnet
• Machine the magnet
• Bend the magnet
• Force-fit it into an undersized recess
• Allow magnets to collide uncontrollably
• Apply excessive sideways leverage

Damaged magnetic fragments may be sharp and should be handled carefully.

Please Note

This product is a Neodymium Cylinder Magnet measuring 4mm in diameter x 20mm long, manufactured from Neodymium Iron Boron (NdFeB) rare earth magnetic material.

No specific NdFeB magnetic grade, coating or plating, pull force, Gauss rating, magnetisation direction, dimensional tolerance or maximum operating temperature has been supplied and these specifications should not be assumed.

Actual magnetic performance depends on magnetic grade, magnetisation direction, target steel thickness and composition, available contact area, air gaps, surface condition and magnetic circuit geometry.

Because this magnet has a long, slender profile, avoid bending, levering or excessive sideways loading. Neodymium is a brittle magnetic material and should not be drilled, cut or conventionally machined.

Small neodymium magnets present a serious ingestion hazard. If more than one magnet is swallowed, they can attract to each other through internal tissue and cause severe or life-threatening injuries. Keep this magnet securely away from babies and children and seek urgent medical attention if ingestion is suspected.

Keep neodymium magnets away from pacemakers and other medical implants, magnetic storage media and sensitive electronic equipment.