Safety Pins (Fokker Pins)

Safety Springs and Fokker Pins for Quick-Release Retaining Connections

Safety springs, also known as Fokker pins, are used to secure pins, shafts, stub axles and other connecting elements with a cross hole. They prevent mounted components from sliding off unintentionally or a retaining pin from moving out of its intended position.

The straight wire section of the Fokker pin is inserted through the existing cross hole. The spring-loaded loop is then placed around the pin or shaft and closed. This keeps the straight retaining section securely inside the hole while allowing the connection to be released again without special tools.

Unlike a conventional split pin, a Fokker pin normally does not have to be bent open or replaced after every removal. Provided that it remains in good condition, it can be used repeatedly. This makes it particularly suitable for connections that need to be opened, adjusted or serviced regularly.

Meaning of the Specifications in the Product Table

The safety spring should not be selected by its overall length alone. The diameter of the pin, position of the cross hole, retaining length and wire diameter are particularly important.

How a Fokker Pin Works

The retaining action is achieved through a combination of positive mechanical retention and spring force.

The straight wire section passes through the cross hole and prevents axial movement of the secured component. The spring-loaded loop then encloses the pin or shaft and prevents the straight section from being pulled out of the hole unintentionally.

For reliable retention:

• the straight leg must pass completely through the cross hole,

• the spring loop must be fully closed,

• the loop must fit correctly around the pin or shaft,

• sufficient space must be available for installation and removal.

A safety spring that is only partially closed or has been permanently stretched does not provide reliable retention.

How to Select the Right Safety Spring

Proceed in the following order:

1. Measure the pin diameter: Inside diameter Di must match the outside diameter of the pin or shaft.

2. Check the cross hole: The hole must be large enough for wire diameter d. An unnecessarily large hole may create additional play.

3. Check the retaining length: L2 must suit the position of the cross hole and the width of the components being secured.

4. Consider the installation space: The spring loop requires sufficient clearance for opening, closing and positioning around the pin.

5. Select the material: Humidity, corrosion, temperature and cleaning media affect the choice of material.

6. Assess the load: The safety spring must be suitable for the expected operating conditions and the importance of the connection.

A Fokker pin is a retaining element, not a load-bearing connecting pin. The actual operating, shear and tensile loads must be carried by the pin, shaft and surrounding components.

Spring Steel or Stainless Spring Steel

Safety springs made from 1.1231 are suitable for many general applications in dry indoor environments. The spring steel provides the elasticity required for opening and closing the loop and allows it to return reliably to its intended shape.

Versions made from 1.4310 offer increased corrosion resistance and are generally more suitable for humid environments, outdoor applications or equipment that is cleaned regularly.

However, stainless spring steel is not resistant to every surrounding medium. Suitability must be checked separately where the spring is exposed to salt water, chlorides, acids or aggressive cleaning agents.

Installation Recommendations

Before installation, the safety spring, pin and cross hole should be clean and free from burrs or other damage.

Insert the straight leg completely through the cross hole. Then guide the spring loop around the pin in a controlled manner and close it fully. After installation, check the secure seating manually.

The Fokker pin must not be forced over a pin that is significantly too large. Excessive opening may cause permanent deformation and reduce the retaining effect.

The installation position should also be selected so that the spring loop cannot catch on adjacent or moving components and be opened unintentionally.

Reuse and Inspection

Before reusing a safety spring, check whether:

• the spring loop still closes securely,

• the wire is not bent or cracked,

• no permanent stretching is visible,

• no significant wear is present,

• corrosion has not impaired the function.

Damaged, deformed or heavily corroded safety springs should be replaced. A new retaining element is recommended for safety-relevant connections.

Typical Applications

Fokker pins are commonly used on:

• stub axles and joint pins,

• trailers and commercial vehicles,

• agricultural machinery,

• construction and garden equipment,

• levers and linkages,

• removable rollers and wheels,

• adjustable fixtures,

• machine and vehicle assemblies.

Further quick-release retaining solutions can be found in our spring elements overview.

Frequently Asked Questions About Fokker Pins

Is a tool required for installation?

Normally not. The safety spring can usually be opened, inserted and closed by hand.

How do I determine the correct size?

The main values are the pin diameter, cross-hole size, retaining length L2, inside diameter Di and wire diameter d.

Can Fokker pins be reused?

Yes, provided that they are not damaged, permanently deformed, worn or heavily corroded.

What is the difference from an R-clip?

Both designs are inserted through a cross hole. A Fokker pin has a closable spring loop that encloses the pin and provides additional protection against the straight retaining section being pulled out.

Can Fokker pins carry high operating loads?

Their main purpose is to prevent the connection from coming apart unintentionally. The actual operating loads must be carried by the load-bearing components.