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In general, a spacer is a solid material used to separate two parts in an assembly. Spacers can vary in size from microns to centimeters. They can be made of metal, plastic, glass, and other materials. Shapes include flat sheet, cylindrical and spherical.
A standoff is a threaded separator of defined length used to raise one part in an assembly above another. They are usually round or hex (for wrench tightening), often made of stainless steel, aluminum, brass, or nylon, and come in male-female or female-female forms. In electronics they are frequently used to raise a 
printed-circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich struc ...
above a surface. Insulating standoffs keep two parts from touching each other, thereby preventing electrical shorts. In some cases (e.g., D-subminiature
The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems.
Description, n ...
connectors), short standoffs may be used to receive the jackscrews
A jackscrew, or screw jack, is a type of jack that is operated by turning a leadscrew. It is commonly used to lift moderately and heavy weights, such as vehicles; to raise and lower the horizontal stabilizers of aircraft; and as adjustable suppo ...
that lock the connection together.
Both Spacers and Standoffs come in Round and Hex shapes with male and female threads. Knurling on the outside surface can also be done to provide sturdier grip.
In contrast, some spacers may look similar to standoffs but are unthreaded pieces of tubing which let the entire bolt pass through. Since they cannot be tightened, they are usually round.
Audio visual equipment (e.g., AV amplifiers) can utilise extra space above or below their mounting in order to achieve extra cooling in the way of better airflow. AV spacers are made for this purpose.https://x-air.co.uk
Usage in home computers
Size 4-40 is used to receivejackscrews
A jackscrew, or screw jack, is a type of jack that is operated by turning a leadscrew. It is commonly used to lift moderately and heavy weights, such as vehicles; to raise and lower the horizontal stabilizers of aircraft; and as adjustable suppo ...
securing cable connectors to external computer ports, and size 6-32 is used for motherboard mounts.
Dell, Inc.
Dell is an American based technology company. It develops, sells, repairs, and supports computers and related products and services. Dell is owned by its parent company, Dell Technologies.
Dell sells personal computers (PCs), servers, data ...
refers to standoffs that receive thumbscrews as "hex nut screws" and measures them with the metric system
The metric system is a system of measurement that succeeded the Decimal, decimalised system based on the metre that had been introduced in French Revolution, France in the 1790s. The historical development of these systems culminated in the d ...
.
See also
*Star filler
A star filler (also known as cross filler, splines, separators and crossweb fillers) is a type of plastic insert in Cat 5 and Cat 6 cable which separates the individual stranded pair sets from each other while inside of the cable. It increases the ...
* Strut
A strut is a structural component commonly found in engineering, aeronautics, architecture and anatomy. Struts generally work by resisting longitudinal compression, but they may also serve in tension.
Human anatomy
Part of the functionality o ...
* Screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
References
Hardware (mechanical) {{tech-stub