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Captive screws are screws specially designed to lock into place on a parent or motherboard, allowing for the easy installation and removal of attached pieces without the release of the screw. They are commonly used in the manufacture of computer parts, furniture, and other goods that need to be made on high volume assembly lines, because such screws are quicker and safer to use than more conventional types, as they don't fall and clog or damage machinery. Many military contractors prefer to use them to meet military standardization requirements and provide easy, safe access to objects needing repair. Captive screws also allow for rapid assembly line manufacture, because they can be installed at different points along the line.
Consumers use captive screws as well, especially on furniture that arrives in a box and needs to be assembled. In such an instance, the screws take the form of small bolts that go through pre-drilled holes and, when turned, grip a protruding nut and lock it into place. They can be released with a twist of a screwdriver, but otherwise, they will remain firmly fixed, and the furniture can be assembled or disassembled around them without fear of the screws falling off and becoming lost. Disassembling furniture put together with this method may require some manipulation to get the screws to release, especially if the furniture has been dropped or twisted, but it is possible with firm traction on a drill or screwdriver to cause the grippers to release the screws.
Captive screws take a variety of forms, including the twist-and-lock variety used on furniture. Some have flanges or nuts that lock onto the parent piece of wood or metal, and others come with clips or rings. In some applications, especially in the computer industry, the screws are soldered directly onto their parent surface, making their installation permanent. Many have a hexagonal head designed to be used with specialized tools, but they also come with standard or Phillips heads designed to be used with ordinary screwdrivers and drill equipment. Captive screws are available in a wide range of sizes and configurations, much like conventional screws, designed for a wide range of applications.
Some screws are designed to retract or pivot back to protect workers from being scraped or cut by them as their parent boards move down the line. Others are designed to mount flush with the object they are installed upon. Because captive screws are not standardized, it is important for people to be careful when trying to interchange two apparently similar types. Small differences in the threading, grooves, or shank may make switching out different screws difficult or inadvisable, depending upon the application.
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