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A cleko, also spelled cleco, is a fastener developed by the Cleveland Pneumatic Tool Company. Widely used in the manufacture and repair of aluminum-skinned aircraft, it is used to temporarily fasten multiple sheets of material together before the pieces are permanently joined.
Fastener and Tool
The basic type consists of a steel cylinder body, a plunger on the top, a spring, a pair of step-cut locks, and a spreader bar. A special type of pliers are used to push in the spring-loaded plunger. This pushes down on the step-cut locks, which pushes them away from the spreader bars and allows them to come together. This allows the user to slip the locking jaws through a hole made through multiple sheets of material. When the plunger is released the spring pulls the locking jaws back towards the spreader bar, which separates the two jaws. The material sheets are then squeezed in between the step-cut area and the steel cylinder. This keeps the holes in the separate sheets aligned. 
Cleko-type fasteners are also available with a threaded mechanism to draw the spreader bar up. Clekos of this type take more time to install and remove, but can be made much tighter than the spring-type clekos. They are commonly available with a wingnut for hand tightening, or with a simple hex nut so that they may be spaced more closely together. In either case they will usually have a hexagonal body that may be better gripped to tighten or release the spreader bar.
Sizes and Colour-coding
Regardless of their form, they are typically colour-coded for ready identification of their size.
|Silver (Zinc)||3/32" (2.4mm)|
|Gold (Brass)||3/16" (4.8mm)|
The most common types of Cleco fasteners are plier operated, wing nut, cylindrical body and hex nut.
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