Dzus fastener
The Dzus fastener, also known as a turnlock fastener or quick-action panel fastener, is a type of proprietary quarter-turn spiral cam lock fastener often used to secure skin panels on aircraft and other high-performance vehicles. It is named after its inventor William Dzus.
The Dzus brand is owned by Southco and fastener Dzus are produced by Southco.
History
The fastener was invented and patented by William Dzus, an American engineer of Ukrainian descent, in the early 1930s.Operation
Functionality
To fasten the cowling to the fuselage, the button's shank is inserted into a hole on the fuselage. A screwdriver is then used to turn the button via a slot in its head. As the button rotates, the spiral slots on the shank act as cams, pulling a spring into position. The projections on the slots resist reverse rotation, preventing the fastener from loosening due to vibration. Optionally, felt or rubber strips can be placed between the cowling and the fuselage to minimize noise.Unfastening
To unfasten the cowling from the fuselage turn the button one-quarter of a turn. This will disengage the button from the spring. The holes are large-enough to allow the spring to clear the projection either while engaging the button or disengaging it. The end of the shank that has the slots must be well-rounded so spring can easily enter its slots.Components
The removable part of the Dzus fastener consists of a button with a head that includes a slot for turning. A groove on the button ensures it remains attached to the cowling when unfastened. The stationary part includes the spring, which is riveted to the fuselage. The spring has arched coils between the rivets, providing the necessary tension for secure fastening.The shank of the button contains spiral bayonet slots that engage the spring. These slots include holes that hold the spring in place once fastened, with projections preventing accidental unfastening. The button’s head is pressed against the cowling, keeping it firmly in place.
Improvements
Over time, several improvements have been made to the Dzus fastener design. Some versions include a housing or bucket around the female part to reduce water ingress. Others have been optimized for ease of use, such as incorporating List of [screw drives|self-centering screwdrivers]. Cost-saving measures, like securing the spring directly to the female hole without rivets, have also been introduced. Additionally, the button is often die-cast in modern versions to reduce manufacturing costs compared to earlier machined versions.Uses
Dzus fasteners are also used to secure plates, doors, and panels that require frequent removal for inspection and servicing. These fasteners are notable in that they are of an "over-centre" design, requiring positive sustained torque to unfasten. Thus, any minor disturbance to the fastener will tend to correct itself rather than proceed to further loosening as it would in threaded fasteners.Turnlock fasteners are available in several different styles and are usually referred to by the manufacturer's trade name. Some of the most common are DZUS, Camloc, and Airloc.