Computer case screws
Encyclopedia
Computer case screw
s are the hardware used to fasten together parts of a computer case
and to fasten the system components (such as motherboard
s, hard drives, and power supplies
) to the case. Although there are numerous manufacturers of computer cases throughout the world, the computer industry has generally standardized on some specific screw thread
measurements. The Unified Thread Standard
(UTS) originates from the United States while the ISO metric screw thread
is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimeter.
6-32 screw holes are often found on expansion cards (such as PCI cards) and hard disk drives. M3 screw holes are often found on optical disc drives and floppy drives. 4-40 jackscrews are often found on connectors at the ends of certain types of cables.
with a major thread diameter of and a pitch (distance between adjacent threads) of . It is by far the most common screw found inside computer cases and commonly appears in lengths of 0.15 and . Nearly every brand new computer case comes with a bag of these. They are used:
Of all the screws provided by computer case manufacturers, the 6-32 screw typically has the coarsest threading. They are almost always provided with a Phillips
drive, accepting a #2 size tip (the larger of the two most common Phillips screwdriver tips). While a #1 size tip will drive the screw, it will be awkward to use and increases the risk of cam-out
and damage to the screw head. They are less frequently provided with a hex head, even less with a pan head - a low disk with a chamfer
ed outer edge. Because they are used in places where easy removal and replacement may be desirable (such as on the side panels of the PC case), they are frequently available as thumbscrews with oversized friction-gripped heads that can be removed with one's fingers rather than with tools.
6-32 screws will fit into holes threaded for M3 screws (the second most common type of screw in PCs), but this will damage the finer M3 threading. Also, when 6-32 screws are screwed into brass M3-threaded motherboard standoffs, the threads tend to become "locked", and the entire motherboard must be removed to separate them.
screwdriver tip.
M3 screws are used for fastening optical disc drives and floppy drives
. They will fit in 6-32-threaded holes, but their narrower diameter and finer thread pitch causes them to seat only loosely in the hole.
M3 screws are also the most common screw used to secure a motherboard to motherboard standoffs.
Of all the screws provided with PCs, M3s are usually identified by them having the finest thread pitch of all the screws provided.
6-32 screws will strip the threads of M3-threaded holes. When the M3 hole is drilled into sheet metal (as on floppy and optical disc drives), a 6-32 screw that damages the threading will typically stay in the hole and can be removed fairly easily. When the M3 threading is into solid metal (such as a motherboard standoff), a 6-32 screw will get stuck before it can be screwed in all the way.
standoffs for attaching the motherboard to the case chassis. Sometimes threaded or snap-lock plastic standoffs are used, which are less secure mechanically. Metal standoffs provide an electrical ground connection between the motherboard and case, while plastic standoffs do not. The standoff provides a margin of space between the motherboard and the case. Without the space, the motherboard would be in physical contact with the case, which would cause it to not function because its various solder points would be in contact with the case's metal, which forms a short circuit with the computer's electrical ground.
There is no rigid standard for what measurements a case's standoffs use. However, use of M3 and 6-32 threads is nearly universal. There is also no single standard for the height of the standoff; one quarter inch is common but not universal.
Each standoff has a "male" portion that screws into the case, and a "female" portion that receives a screw that has passed through a specially grounded pre-drilled hole in the motherboard. Standoffs that use strictly M3, strictly 6-32, or a combination (male portion 6-32, female portion M3) are all fairly common.
It is good practice to tighten the standoff to the chassis with a nut driver
or pliers, or use a thread locking compound between the male portion of the standoff and the chassis sheet metal. This ensures that if when detaching the motherboard, the screw that holds the motherboard onto the standoff will unfasten instead of the standoff becoming unfastened from the chassis. If tightening the standoff with a nut driver or pliers, be careful not to over-tighten, as the soft metal threads of the standoff and chassis are easily stripped or broken. Using a thread locking compound between the motherboard fastening screw and the female portion of the motherboard standoff is neither needed nor desired. Thread locking compound will not adversely affect the electrical ground path between the motherboard and chassis.
It is a frequent mistake when building PCs to accidentally use 6-32 threaded screws into motherboard standoffs expecting an M3 screw. The result is that the screw will not go all the way, and the threads become stripped and "lock". Once locked, attempts to remove the top screw typically result in the entire standoff unscrewing from the case and potentially flexing the motherboard. In that situation, the screw and the standoff cannot be separated without removing the entire motherboard and subjecting it to potential damage while it is flexed in place.
s are used to fasten certain connectors
to hardware port
s. The screws are typically located on either side of D-subminiature
connectors such as on VGA
, serial
, parallel
, and legacy
game controller ports
. They are also more recently used on DVI
connectors. The female
4-40 is usually just a removable standoff that has been screwed into the port with a relatively tight torque
. The standoff can be unscrewed or tightened using a hex driver. This standoff also often serves as a mechanical mounting either attaching a connector on a flylead to the case or attaching the backplate to an expansion card (connectors on the ATX IO plate are not normally attached to the plate). The screw has 40 threads per inch, and despite its threads appearing similar to M3, they are not interchangeable. Comparing them in SI units, the 4-40 has a pitch of while the M3 has a finer pitch of .
A typical length for a 4-40 screw used in PCs is .
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
s are the hardware used to fasten together parts of a computer case
Computer case
A computer case is the enclosure that contains most of the components of a computer...
and to fasten the system components (such as motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
s, hard drives, and power supplies
Power Supply Unit (Computer)
A power supply unit converts mains AC to low-voltage regulated DC power for the internal components of the computer. Modern personal computers universally use a switched-mode power supply...
) to the case. Although there are numerous manufacturers of computer cases throughout the world, the computer industry has generally standardized on some specific screw thread
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
measurements. The Unified Thread Standard
Unified Thread Standard
The Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...
(UTS) originates from the United States while the ISO metric screw thread
ISO metric screw thread
The ISO metric screw threads are the world-wide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.-Basic profile:...
is standardized worldwide. In turn, these thread standards define preferred size combinations that are based on generic units—some on the inch and others on the millimeter.
6-32 screw holes are often found on expansion cards (such as PCI cards) and hard disk drives. M3 screw holes are often found on optical disc drives and floppy drives. 4-40 jackscrews are often found on connectors at the ends of certain types of cables.
6-32 screw
The 6-32 is a UTS screwUnified Thread Standard
The Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...
with a major thread diameter of and a pitch (distance between adjacent threads) of . It is by far the most common screw found inside computer cases and commonly appears in lengths of 0.15 and . Nearly every brand new computer case comes with a bag of these. They are used:
- To fasten a power supply to the case
- To fasten a hard disk drive to the case
- To hold an expansion cardExpansion cardThe expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or backplane to add functionality to a computer system via the expansion bus.One edge of the expansion card holds the contacts that fit exactly into the slot...
in place by its metal slot cover - To fasten case components to one another
- Usually, a 6-32 screw holds the main cover on the case. When it's not a 6-32, a larger 8-32 is the most likely alternative.
Of all the screws provided by computer case manufacturers, the 6-32 screw typically has the coarsest threading. They are almost always provided with a Phillips
Henry F. Phillips
Henry F. Phillips was a U.S. businessman from Portland, Oregon. The Phillips-head screw and screwdriver are named after him....
drive, accepting a #2 size tip (the larger of the two most common Phillips screwdriver tips). While a #1 size tip will drive the screw, it will be awkward to use and increases the risk of cam-out
Cam out
To cam out is a process by which a screwdriver slips out of the head of a screw being driven once the torque required to turn the screw exceeds a certain amount....
and damage to the screw head. They are less frequently provided with a hex head, even less with a pan head - a low disk with a chamfer
Chamfer
A chamfer is a beveled edge connecting two surfaces. If the surfaces are at right angles, the chamfer will typically be symmetrical at 45 degrees. A fillet is the rounding off of an interior corner. A rounding of an exterior corner is called a "round" or a "radius"."Chamfer" is a term commonly...
ed outer edge. Because they are used in places where easy removal and replacement may be desirable (such as on the side panels of the PC case), they are frequently available as thumbscrews with oversized friction-gripped heads that can be removed with one's fingers rather than with tools.
6-32 screws will fit into holes threaded for M3 screws (the second most common type of screw in PCs), but this will damage the finer M3 threading. Also, when 6-32 screws are screwed into brass M3-threaded motherboard standoffs, the threads tend to become "locked", and the entire motherboard must be removed to separate them.
M3 screw
This screw is the second most common screw found in PCs. This is a metric screw, and just about every case manufacturer provides a package of M3 screws as well as 6-32's. Specifically, the screw type is M3-0.50, meaning the threads of the screws are apart. These screws, like the 6-32 screws, also typically accept a #2 size PhillipsHenry F. Phillips
Henry F. Phillips was a U.S. businessman from Portland, Oregon. The Phillips-head screw and screwdriver are named after him....
screwdriver tip.
M3 screws are used for fastening optical disc drives and floppy drives
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
. They will fit in 6-32-threaded holes, but their narrower diameter and finer thread pitch causes them to seat only loosely in the hole.
M3 screws are also the most common screw used to secure a motherboard to motherboard standoffs.
Of all the screws provided with PCs, M3s are usually identified by them having the finest thread pitch of all the screws provided.
6-32 screws will strip the threads of M3-threaded holes. When the M3 hole is drilled into sheet metal (as on floppy and optical disc drives), a 6-32 screw that damages the threading will typically stay in the hole and can be removed fairly easily. When the M3 threading is into solid metal (such as a motherboard standoff), a 6-32 screw will get stuck before it can be screwed in all the way.
Motherboard standoff
Most cases use threaded brass male-femaleGender of connectors and fasteners
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...
standoffs for attaching the motherboard to the case chassis. Sometimes threaded or snap-lock plastic standoffs are used, which are less secure mechanically. Metal standoffs provide an electrical ground connection between the motherboard and case, while plastic standoffs do not. The standoff provides a margin of space between the motherboard and the case. Without the space, the motherboard would be in physical contact with the case, which would cause it to not function because its various solder points would be in contact with the case's metal, which forms a short circuit with the computer's electrical ground.
There is no rigid standard for what measurements a case's standoffs use. However, use of M3 and 6-32 threads is nearly universal. There is also no single standard for the height of the standoff; one quarter inch is common but not universal.
Each standoff has a "male" portion that screws into the case, and a "female" portion that receives a screw that has passed through a specially grounded pre-drilled hole in the motherboard. Standoffs that use strictly M3, strictly 6-32, or a combination (male portion 6-32, female portion M3) are all fairly common.
It is good practice to tighten the standoff to the chassis with a nut driver
Nut driver
A nut driver is a tool for tightening nuts and bolts. It essentially consists of a socket attached to a shaft and cylindrical handle and is similar in appearance and use to a screwdriver. They generally have a hollow shaft to accommodate a shank onto which a nut is threaded...
or pliers, or use a thread locking compound between the male portion of the standoff and the chassis sheet metal. This ensures that if when detaching the motherboard, the screw that holds the motherboard onto the standoff will unfasten instead of the standoff becoming unfastened from the chassis. If tightening the standoff with a nut driver or pliers, be careful not to over-tighten, as the soft metal threads of the standoff and chassis are easily stripped or broken. Using a thread locking compound between the motherboard fastening screw and the female portion of the motherboard standoff is neither needed nor desired. Thread locking compound will not adversely affect the electrical ground path between the motherboard and chassis.
It is a frequent mistake when building PCs to accidentally use 6-32 threaded screws into motherboard standoffs expecting an M3 screw. The result is that the screw will not go all the way, and the threads become stripped and "lock". Once locked, attempts to remove the top screw typically result in the entire standoff unscrewing from the case and potentially flexing the motherboard. In that situation, the screw and the standoff cannot be separated without removing the entire motherboard and subjecting it to potential damage while it is flexed in place.
4-40 jackscrews
Pairs of 4-40 UTS jackscrewJackscrew
A jackscrew is a type of jack which is operated by turning a leadscrew. In the form of a screw jack it is commonly used to lift heavy weights such as the foundations of houses, or large vehicles.-Advantages:...
s are used to fasten certain connectors
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...
to hardware port
Computer port (hardware)
In computer hardware, a port serves as an interface between the computer and other computers or peripheral devices. Physically, a port is a specialized outlet on a piece of equipment to which a plug or cable connects...
s. The screws are typically located on either side of D-subminiature
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 smaller connectors used on computer systems....
connectors such as on VGA
VGA connector
A Video Graphics Array connector is a three-row 15-pin DE-15 connector. The 15-pin VGA connector is found on many video cards, computer monitors, and some high definition television sets...
, serial
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
, parallel
Parallel port
A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
, and legacy
Legacy system
A legacy system is an old method, technology, computer system, or application program that continues to be used, typically because it still functions for the users' needs, even though newer technology or more efficient methods of performing a task are now available...
game controller ports
Game port
The game port is a device port found on IBM PC compatible systems throughout the 1980s and 1990s. It was the traditional connector for joystick input devices until superseded by USB in the 21st century....
. They are also more recently used on DVI
Digital Visual Interface
The Digital Visual Interface is a video interface standard covering the transmission of video between a source device and a display device. The DVI standard has achieved widespread acceptance in the PC industry, both in desktop PCs and monitors...
connectors. The female
Gender of connectors and fasteners
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...
4-40 is usually just a removable standoff that has been screwed into the port with a relatively tight torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
. The standoff can be unscrewed or tightened using a hex driver. This standoff also often serves as a mechanical mounting either attaching a connector on a flylead to the case or attaching the backplate to an expansion card (connectors on the ATX IO plate are not normally attached to the plate). The screw has 40 threads per inch, and despite its threads appearing similar to M3, they are not interchangeable. Comparing them in SI units, the 4-40 has a pitch of while the M3 has a finer pitch of .
A typical length for a 4-40 screw used in PCs is .