Fasteners that remain attached to the panel or parent material, even when disengaged from the mating part, are captive screws. They are used to meet military requirements, prevent screws from being lost, speed assembly and disassembly operations, and prevent damage from loose screws falling into moving parts or electrical circuits.
Methods used to attach captive screws to the parent material include split washers clipped on after the screw has been inserted in the panel; threaded panel holes used in conjunction with a screw that has an externally relieved shank, a long groove between the head and threads; or a ferrule or sleeve that is pressed, threaded, swaged, or flared to the parent material.
Captive screws are available with either inch or metric threads, and with most of the common finishes and head styles available in ordinary machine screws. Because there are no universally accepted standards for captive screws, many apparently similar captive screws are not interchangeable with each other.