By Dieter Jüling

1. About Quarter Turn Fasteners

1.1 Introduction

A quarter (¼) turn fastener is a mechanically locking quick-release fastener that consists of a stud, retainer and receptacle; offering the ability to open and close with a simple 90° (quarter turn) action. Quarter turn fasteners require a spring element to enable them to create a pre-load (the internal load applied to a fastener as a result of its being installed, before any external load). They were originally invented in the 1930’s as an easy open alternative to standard nuts and bolts.

Depending on the fastener type and mounting requirements; the spring element can be part of the stud assembly or incorporated in the receptacle. Stud assemblies with snap-in grommets are available on some series giving a captive assembly without the need for a retaining washer and subsequent assembly from the back side.

1.2 Applications – where are they used?

Quarter turn fasteners are ideal fasteners for panels or compartments that need to be opened or closed regularly because only a quarter turn movement (rotating the stud 90°) and a captive configuration is required for operation.

The robust and safe operation makes quarter turn fasteners suitable for a wide variety of applications, including (but not limited to) trains, trucks, agriculture, racing, helicopter aircraft interior, streetlamps, stage lighting.

Captive applications are found in aircraft, production machines or in streetlamps, where the loss of the fastener in these applications would be extremely critical.

In applications where vibration can pose a threat to the performance of other fasteners, such as machinery, trucks, agriculture and trains; excellent vibration resistance is guaranteed with quarter turn fasteners.


2. Operation and design principles of quarter turn fasteners

2.1 How it Operates

When the stud assembly is rotated, the stud cross pin rides up the cam causing a controlled joint preload to be applied. This action is accomplished by rotating the stud by approximately 90°. At this point a positive mechanical stop is reached and the cross-pin falls into the locking detent.

In combination with the preload this mechanism provides a vibration-proof connection – a factor that made it ideal for its’ original purpose of fastening helicopter panels in high vibration environments.

2.2 Design Principles

Quarter-turn fasteners connect components under an elastic preload. The spring element to produce the preload can be part of the stud or receptacle.

Fastener tensile loads (specified in the catalogue) are reached after overcoming the spring element generated preload. Unlike threaded fasteners, Camloc fasteners do not rely on the elasticity of joint and fastener materials to accomplish preload. Due to a much lower installation torque the stud recess is exposed to much lower wear and therefore capable of a much higher number of cycles.

The stud assembly or receptacle is designed with a spring element which allows repeated application of controlled preload with assured reliability over a high number of cycles.

2.3 Advantages of the Camloc 1/4-Turn Fastener

  • Efficient: offering quick and easy access for maintenance panels through simple quarter turn operation.
  • Reliable: offering a secure and safe, vibration-resistant quick release fastener system.
  • Versatile: available in a wide range of sizes, in a variety of materials and to suit many different surface types, plus with head styles to suit either hand or tool operations.
  • Cost-reducing: long life with a high number of operating cycles, plus reduced assembly costs compared to alternative fastening types.

Camloc can also offer a special solution to resolve fastening issues in the most challenging applications. To speak to an engineer, please Contact Us.