Captive Fasteners: Their Uses and Types
Fasteners are important components for numerous applications, allowing for two or more parts to be secured together to prevent their separation. When there is a need for retaining a fastener’s position within an installation, there are a number of fastener types or methods that may be employed. Captive fasteners in particular are specialized fastener types that are specifically engineered to retain a permanent hold when installed, even maintaining its installation upon servicing. They are often used for the means of deterring the loss of a fastener or damage that results from loose parts, and they can come in varying forms depending on the need and application.
The captive screw is one of the most common variations, and they are a special screw capable of achieving a permanent hold within the component through their locking feature. While they retain the external threading and head of a conventional screw, the captive type is actually able to be unfastened and fastened without its removal from the pilot hole. This allows for the screw to remain within the pilot hole while also freeing the surfaces that were previously secured. A captive screw is capable of retaining its position in a material through the use of cold forming, that of which fuses the parts into a single element.
For their use, captive screws are often found within PCBs and panel assemblies which are present within signs, medical devices, network cabinets, and more. Due to their threaded end and unthreaded shank, a captive fastener may be locked into a preformed hole and unfastened without the need for removal. Captive screws are also regularly paired with other fasteners and components, those being springs, washers, and retainers which all help form the self-captivating assembly. With their locking capabilities, captive screws are most often employed for the means of combating vibration shock, thermal expansion, and thermal conductivity.
Captive nut fasteners are another common type that may be seen in various assemblies, and they are internally threaded. Unlike a standard nut, captive nut designs feature a spring steel cage that encapsulates the fastener, and they are specifically designed to easily connect with studs. Captive nuts are also beneficial for blind installations, and they pose little risk to the finishes of panels. Captive nuts may commonly be found within industrial and electronic applications to prevent the loosening of fasteners.
Beyond such common examples, other captive fasteners include captive studs, captive pins, captive standoffs, and other such components. The captive stud is one in which externally threading is provided, and they are permanently integrated on an assembly and may provide retention for outer-surface housing attachments. With a captive pin, the fastener may be pushed into the hole of an electronic circuit board, and they have self-clinching heads that retain their position through the resistance of toque and push-out forces. The captive standoff is an internally threaded fastener, and it is often paired with a mating screw for the means of securing, supporting, or providing space for circuit boards.
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