A captive screw describes, in general, a screw which remains attached to a panel even when its threads are not engaged. This is usually accomplished with the use of a retaining washer or similar method which prevents the disengaged screw from falling back out through its installation hole. The overriding benefit of captive panel screws in the field is the prevention of lost fasteners on access panels and doors, especially in those applications where safety and security are major considerations. Most captive panel screws share the following characteristics: machine screw threads, a head, and an unthreaded shank, between the head and the threads, with a diameter at or below the minor diameter of the threads. There are no current consensus standards for this category. Determining the exact dimensions and the type of captive screw required is the result of a number of different considerations, mostly dictated by the application. Many designs include characteristics such as knurled sides, shouldered bearing surfaces, slotted heads, wide heads, narrow heads and pointed ends.