Safety Ring DIN 471

Retaining and Locking Elements for Shafts, Bores and Bolted Joints

Retaining and locking elements prevent components from moving unintentionally during operation or stop bolted joints from loosening under vibration and dynamic loads. Different operating principles are used depending on the design and the type of connection that needs to be secured.

Circlips to DIN 471 and DIN 472 are installed in a groove and provide positive axial retention. Wedge-locking washers to DIN 25201, by comparison, are installed in pairs beneath a bolt head or nut and prevent the bolted joint from rotating loose.

The Febrotec range includes:

• circlips for shafts to DIN 471,

• circlips for bores to DIN 472,

• wedge-locking washers to DIN 25201.

These products are used in mechanical engineering, drive technology, automotive engineering, plant construction, fixture manufacturing, maintenance and many other industrial applications.

Circlips for Shafts to DIN 471

Circlips to DIN 471 are used to retain components axially on shafts. They are fitted externally over the shaft and engage in a machined shaft groove.

The section of the circlip projecting from the groove forms an axial shoulder. Components can rest against this shoulder, including:

• rolling bearings,

• gears,

• pulleys,

• bushes,

• levers,

• spacer washers,

• coupling components.

During installation, the circlip is expanded in a controlled manner using suitable circlip pliers inserted into the two mounting holes. It can then be passed over the shaft and positioned in the groove. When the pliers are released, the ring springs back and seats in the shaft groove.

Selection is primarily based on the nominal shaft diameter. The groove diameter, groove width, ring thickness, free ring diameter and permissible axial load must also be taken into account.

A circlip with a nominal size of 20 mm, for example, is intended for a shaft with a nominal diameter of 20 mm. The actual groove diameter is smaller than the shaft diameter and must be manufactured according to the applicable product or standard dimensions.

Circlips for Bores to DIN 472

Circlips to DIN 472 are used for the axial retention of components inside a bore or housing. They are compressed, inserted into the bore and then allowed to expand into a groove machined into the bore wall.

The section of the ring projecting inwards from the groove forms an axial contact surface. This allows bearings, bushes, seals, covers and other components to be positioned and retained inside a housing.

Typical applications include:

• bearing housings,

• gearbox housings,

• hydraulic and pneumatic components,

• rollers and hubs,

• pumps,

• electric motors,

• technical housings and fixtures.

For installation, the circlip is compressed using suitable internal circlip pliers. After insertion, it must be able to expand completely into the groove.

Selection is based on the nominal bore diameter. The groove diameter, groove width, material thickness, free ring diameter and permissible axial load must also match the design.

Circlips to DIN 471 and DIN 472 may appear similar, but they are not interchangeable. A shaft circlip is expanded for installation, whereas a bore circlip is compressed.

Wedge-Locking Washers to DIN 25201

Wedge-locking washers secure bolted joints against self-loosening caused by vibration and dynamic loading. They are always used as a matched pair.

The inner faces of the pair have wedge-shaped cams. The outer faces have radial serrations that engage with the bolt head or nut and with the contact surface of the component.

If the bolted joint attempts to rotate loose, movement must occur across the internal wedge surfaces. Due to the wedge geometry, this movement would increase the distance between the bolt head or nut and the contact surface. The bolt would therefore have to be stretched further. This counteracts the rotational loosening movement and helps maintain the preload in the joint.

Wedge-locking washers are particularly suitable for bolted joints used in:

• machines and production equipment,

• commercial and rail vehicles,

• construction machinery,

• wind turbines,

• conveyor and lifting equipment,

• pumps and compressors,

• vibrating drives,

• safety-relevant structures.

Selection is primarily based on the thread size. It must also be determined whether a standard version or a washer pair with an enlarged outside diameter is required.

A larger outside diameter may be useful for slotted holes, oversized clearance holes, soft contact surfaces, flange bolts or other applications where the load needs to be distributed over a larger area.

Which Retaining or Locking Element Is Suitable?

The correct product group depends on the type of connection and the movement that must be prevented.

Circlips cannot replace wedge-locking washers, and wedge-locking washers cannot replace circlips.

Circlips form a positive axial stop within a groove. They prevent a component from moving along a shaft or within a bore. Wedge-locking washers, by comparison, are used to maintain the preload of a bolted joint and counteract an unwanted rotational movement.

How to Select the Right Circlip

At least the following points should be checked when selecting a circlip:

1. Shaft or bore: First determine whether the component is to be retained externally on a shaft or internally inside a bore.

2. Nominal diameter: The shaft diameter or bore diameter determines the nominal circlip size.

3. Groove dimensions: The groove diameter and width must match the selected circlip.

4. Axial load: The operating force must not exceed the permissible load of the circlip and groove.

5. Material and surface finish: Corrosion, temperature and surrounding media must be considered.

6. Installation access: Sufficient space must be available for the pliers and the required opening or closing movement.

The load capacity of a retaining connection does not depend on the circlip alone. The material strength, groove geometry, edge distance and contact surface of the retained component also influence the capacity of the complete assembly.

A load value stated in a product table should therefore not automatically be treated as the permissible load of the complete construction without further assessment.

Installation Recommendations for Circlips

For reliable installation, we recommend:

• using circlip pliers suitable for the ring size and type,

• expanding or compressing the ring only as far as necessary,

• cleaning the groove before installation,

• removing chips, dirt and foreign particles,

• avoiding burrs and damage on the shaft, bore and groove,

• checking that the ring is fully seated after installation,

• not reusing rings that are deformed or have been overstretched.

The circlip must be correctly seated around its complete circumference. A ring that has engaged only partially may come loose or jump out of the groove under load.

Suitable tools should also be used during removal. Levering out a circlip with screwdrivers or other unsuitable tools can damage the ring, the groove and surrounding components.

Eye protection is recommended during installation and removal because an incorrectly handled circlip may spring away under tension.

Installation Recommendations for Wedge-Locking Washers

Wedge-locking washers must be installed as a complete pair. The cam surfaces face each other on the inside, while the radial serrations face the bolt head or nut and the contact surface.

The following points should be observed:

• always use a complete matched washer pair,

• do not separate the washers for installation,

• do not reverse their orientation,

• select the correct size for the bolt and contact surface,

• use the specified tightening torque for the bolted joint,

• check the thread and contact surfaces before assembly,

• inspect the joint after installation.

Wedge-locking washers do not replace the correct technical design of a bolted joint. Bolt strength, engagement length, preload, friction conditions, tightening method and operating load must all be suitable for the application.

The washers should normally be installed directly beneath the bolt head and nut. Additional loose washers between the wedge-locking pair and the contact surface may prevent the outer serrations from engaging correctly.

Materials and Corrosion Protection

The circlips in the Febrotec standard range are manufactured from spring steel, including material 1.1248. The spring properties of the material allow the elastic deformation required for installation and secure seating in the groove.

Wedge-locking washers are manufactured from hardened or spring-hard steel and are available with a zinc-flake coating. This coating improves corrosion resistance and is suitable for many industrial environments.

The actual resistance of any surface treatment depends on humidity, temperature, salt exposure, cleaning agents and other environmental conditions. For highly corrosive environments, the suitability of the selected material and coating must be assessed separately.

A stainless version may be required for applications in food-processing equipment, outdoor installations, marine environments or areas exposed to aggressive cleaning agents. Material compatibility between the locking element, fastener and surrounding components should also be considered to avoid contact corrosion.

Frequently Asked Questions About Retaining and Locking Elements

What is the difference between DIN 471 and DIN 472?

DIN 471 applies to circlips for shafts. DIN 472 applies to circlips for bores and housings.

Can a shaft circlip be used inside a bore?

No. The geometry and installation direction are different. A circlip designed for bores to DIN 472 must be used for internal retention.

Is a groove required for a circlip?

Yes. Circlips to DIN 471 and DIN 472 require a correctly dimensioned groove in which they can engage positively.

Are wedge-locking washers installed individually?

No. They function only as a matched pair with the wedge-shaped cam surfaces facing each other.

Can a circlip be reused?

A circlip should only be reused if it has not been overstretched, deformed, damaged or affected by corrosion. A new circlip is recommended for safety-relevant applications.

Do wedge-locking washers replace the correct tightening torque?

No. The bolted joint must still be tightened to the specified preload or tightening torque. The washer pair helps prevent rotational loosening during operation.