Captive Fasteners

Captive fasteners are used to meld with the material into which they are joined through a process known as cold forming. Captive fasteners are available in three basic categories: self-clinching fasteners (used for ductile materials), broaching fasteners (used for non-ducticle materials), and weld nuts (used for sheet metal). Each type of captive fastener becomes a permanent part of the panel or item to which it is installed. This permanent installation eliminates loose hardware problems. Both a self-clinching fastener or a broaching fastener will withstand high push-out and torque-out forces. Weld nuts self pilot into pre-drilled holes and are round, thus eliminating need for indexing. A weld nut is best suited for applications needing high strength.

Regardless of type, a captive fastener is installed by pressing the fastener into a pre-drilled or punched hole. Next, a squeezing force is applied to embed the fastener in the panel. The squeezing process causes displaced panel material to flow into the shank of the fastener (through a cold flow process) locking the fastener to the panel. The amount of time that force is applied to captive fasteners is important; enough time must be allowed for the material to flow. Because of this, hammers cannot be used to apply force to the captive fastener as the force does not last long enough for the cold flow process to take place.

Captive fasteners are valuable as they add speed during initial assembly and field servicing, thus keeping costs low. Generally captive fasteners use less space and require fewer assembly operations than caged or anchor nuts. Captive fasteners can be used whenever a component must be easily replaced or where hardware cannot be accessible. It is important to keep in mind that the fastener must be compatible with the panel or sheet material being used. In addition, the hardness of the fastener must be greater than the hardness of the panel material.

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Part Numbers for Captive Fasteners