Captive Screw Description
What is a Captive Screw
Captive screws are used to secure mounting screws to the device so they are not dropped or lost when the screws are undone.
Captive screws may be found on card front panels which are used to secure the front panels to the equipment chassis. If a door is used to hide or protect the cards within the chassis, than captive screws may also be found securing one or more sides of the door. Captive screws may also be found on a front panel of a module to secure a chassis to an equipment rack, so as the module is removed from the rack the screws stay with the chassis and not set aside.
There are a number of installation styles, including press-in, flare-in, snap-in, and floating Captive Screws.
Captive Screw Manufacturers
Above Board
Electronics
{Captive Panel Screws}
Alcoa Inc.
{Captive Panel Screws}
ASM
{Binding Head, Extended Knurled, Fillister, Flat Head, Knobbed}
Keystone Electronics Corp.
{Stainless steel 4-40, 6-32, 8-32 Threads}
Northern Technologies Corp
{#4-40, RoHS, Captive Screws}
Southco.
{Captivation styles, Spring-ejected, Miniature, heat transfer, Captive Nuts}
Next Topic; Equipment Chassis Finish
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Specifying an Equipment Chassis Chassis Design Guide Lines Index
Design Recommendation; Captive screws work best for equipment used out in the field, where a dropped screw may not ever be found leaving the chassis with one less mounting screw. In some cases, in colder regions, a technician my be required to wear gloves in which case it's extremely difficult to hold onto a small screw. When a captive screw is used there is no danger of dropping or losing a screw. Once an enclosure seal is compromised there is little an operator can do. The missing screw could cause air flow problems dust or water intrusion or even EMI issues.
These comments hold true for utilizing Chained Connector Dust Caps as well.
