Socket screws, also known as socket head cap screws, are a type of fastener commonly used in various applications. They are distinguished by their head, which has a recessed drive or socket, allowing them to be tightened or loosened with the appropriate tool. The most common types of socket drives include hex (Allen), Torx, and square drives.
Socket Head Cap Screw (SHCS): This is the most common type, featuring a cylindrical head with a flat top and a recessed socket drive.
Button Head Cap Screw (BHCS): Similar to SHCS but with a rounded top.
Flat Head Cap Screw (FHCS): Flat head with a countersunk design, allowing it to sit flush with the surface.
Hex (Allen) : Requires an Allen wrench or hex key for tightening.
Torx (Star) : Uses a star-shaped pattern and a Torx wrench.
Square Drive : Requires a square-headed driver.
Materials : Socket screws are available in various materials, including stainless steel, alloy steel, and carbon steel. The material choice depends on the application and environmental conditions.
Applications : Socket screws are commonly used in machinery, automotive, electronics, and other industries where a strong and reliable fastening solution is required.
Advantages : The recessed socket drive provides a clean and finished appearance.
High tensile strength and resistance to vibration, making them suitable for critical applications.
They are available in various lengths and sizes to accommodate different needs.
Socket screws are a type of screw designed and manufactured with a hexagonal (hex) internal drive built into the head. As such, they are intended to be tightened and loosened with an Allen wrench or hex key, as opposed to a traditional screwdriver. This is the key feature that sets a socket screw apart from other screw head drive styles such as the Phillips head screw, slotted and flathead screws, and Pozidriv screws, to name just a few.
Another common distinction is that socket screws are often squared off at the tip. These are generally referred to as flat point socket screws and they tend to be the most widely used type found in many common applications. However, it's worth noting that various other designs are also available.
In most other regards, there isn’t typically much physical difference between socket screws and regular screws for the majority of everyday uses. So what exactly is the point of a socket screw, and when should you use one?
The potentially higher torque and clamping force that can be achieved with a socket screw over a regular screw makes them a preferable option in some applications. When compared to regular screws and bolts in a like for like test, socket screws can often deliver some or all of the following advantages in relevant scenarios:
Since socket screws typically offer greater clamping force than standard screws and many other small-format fastener types, fewer socket screws can be used in a given application to achieve the same overall clamping force on the joint or workpiece. Using fewer screws means:
The trend towards lightweight constructions when using socket screws is further enhanced due to their smaller individual size than many other screw types and fastening components - especially compared to nut and bolt fixing arrangements. In particular, the cylindrical heads and internal drives of socket screws are far smaller in diameter than fasteners with external hex heads, and therefore need less space (with no additional room needed to manoeuvre a wrench) for installation.
The average socket cap screw head is around 1.5 times the diameter of the screw shank, and about as high as the shank is wide. However, alternative head designs for socket head cap screws include low head, button head and flat head varieties, intended for driving into countersunk holes and other application-specific mounting positions.
When looking to buy socket screws, note that the stated length of the product is typically measured from immediately under the head to the tip. This is the case for most screw types, but some specific varieties - thumb screws, for example - will often give stated length measurements that include the height of the head in the overall specification.
Most socket screw types are available in either metric or imperial measurements for length and diameter, depending on the particular manufacturer or supplier in question. Many leading brands and socket screw manufacturers will often provide a socket screw sizing chart or similar tool that can be referred to at the point of purchase.
While relatively small socket screw sizes (of diameters ranging from M2 to M6, and lengths of around 3mm to 20mm) tend to be more in demand across a wider range of tasks and applications, the full range of available sizes is considerable. Larger, heavier gauge and extra-long socket screws are not at all uncommon, particularly in widths of around M8 to M20, and lengths of anywhere up to 130mm.
Extra-long socket screws are often found in electrical plug sockets. Common electrical socket screw sizes include 40mm, 50mm, 60mm, 75mm and 100mm.
There are many different materials used in the manufacture of socket screws. The most common materials are steel and stainless steel but alternatives include brass, aluminium, black nickel, zinc-plated and chrome socket screws. The ideal material to choose will depend on the specific application where the socket screw will be used.
Some of the most common socket screw materials are detailed below.
Aluminium socket cap screws are often preferred for applications in which weight is a key consideration. This might include applications ranging from the automotive industry through to uses such as installing hardware and trim on moveable furniture, cabinets, doors and windows.
Despite only being around one third the weight of steel, aluminium is durable and tends to have lower shear strength. While aluminium offers decent performance in terms of corrosion resistance in more challenging environments, it is less hardwearing than stainless steel.
The primary reason why so many steel socket cap screw sets are available with zinc or nickel plating options is for the superior corrosion (rust) resistance this simple manufacturing process can offer screws of all types.
Combined zinc-nickel plating is generally considered to be a tougher coating (up to twice the hardness) when compared to standard zinc plating, and it can also deliver up to four times the corrosion resistance of other metallic coating processes. However, it is typically more expensive, and may not be considered a cost-effective option in many applications where standard galvanised steel socket screws would suffice.
Brass socket cap screws might often be preferred for their aesthetic value, but as an alloy of copper and zinc, brass or brass-tipped socket screws may offer further advantages in certain situations. Brass is stronger than copper alone, although it will still be considerably less rigid than most varieties of steel or stainless steel socket screws.
However, it's also worth noting that brass plating will be less resistant to corrosion than solid brass socket screws. If the product will be used in an exposed location or outdoor application, solid brass socket screws are the preferable option.
As well as different materials, socket screws are also available in different types:
Button head socket cap screws are also known as round head or dome head socket screws. They are manufactured with a smooth, slightly rounded dome at the head, which tends to be somewhat larger and more bulbous than standard cap screw varieties.
Often, this means that a button head socket screw can accommodate a larger gauge of hex key or driver, and thus can be affixed with more torque to achieve greater clamping forces. However, smaller sized hex socket button screws should be fastened with less torque.Button socket screws can also be supplied with tamper-proof drives.
Hex socket countersunk screws, also known as flat or flat head socket screws, are used in applications where it is vital that the installed screw sits flush with or just below the surface of the workpiece.
Countersunk socket screws feature a sloping shoulder design - usually at a standard angle of around 82 degrees - that allows the screw to bed down into the surface via a pre-drilled countersunk hole. Again, they are available in numerous lengths and widths and are widely available under both imperial and metric socket screw sizing charts.
Socket head cap screws contribute in important ways in carrying out modern design techniques which call for smooth contours and surfaces, elimination of clumsy, bulky parts and use of lighter constructions as they apply to flanges, lugs, pockets, and cover plates. Because Screws are made of alloy steel and scientifically heat treated, they are stronger than conventional screws, size for size. Hence, fewer screws – or smaller screws – are required to fulfill a given holding assignment. cap screw is comparable in strength to an ordinary screw of the next larger standard diameter.
Low Head socket head cap screws are high strength, precision fasteners that are designed to be used in applications where head height is a problem. Because of their reduced head height and smaller socket size, they cannot be preloaded as high as a standard socket head cap screw.
Low Head Socket Head Cap Screws are threaded fasteners with a reduced height cylindrical head and a recessed hexagon drive. Metric Low Head Socket Head Cap Screws are turned by using a hexagon shaped key
Button flange head socket cap screws feature a built-in washer, the wide flange keeps the screw head from crushing thin or soft materials. Button flange head socket cap screws are fully threaded and have a Class 3A thread fit. Head height is measured from the bottom of the flange to the top of the head.
Flange button socket screws from ITA Fasteners are protective fasteners which provide the assembly with structural support as well as a visually appealing look. It protects the components around it from damages like scraps and unintentional cuts. Another advantage of these screws is the large under head bearing surface - this eliminates the need for washers. It could also be considered as a built-in washer. These screws are fully threaded to provide its users with grip and accurate positioning.
As mentioned, socket screws are most often associated with machinery and heavy-duty construction. However, they can be used in a wide range of applications, both indoors and out.
Some typical socket screw applications include: