The Types of screws Can be classified according to head, material, function and utility, having in total more than 36 classes.
The screws are fasteners used to join two or more pieces temporarily or permanently. These are extremely important elements in the structures, since it is a system of secure and detachable attachment.
The screws consist of two basic parts that are the head and the stem. And on the stem are two more distinctive elements. A smooth part, which is called a neck and a final stretch known as a thread.
The head is the part of the screw that allows the existence of different types of pieces. This is because the shape of the screw head is what determines the tool to be used for the tightening of the part. There are several types of screws, and these can be divided according to their head, material, finish, utility and function.
According to his head
With hexagonal head
This is one of the most commonly used screws. As its name indicates, it has a hexagon-shaped head and is usually used for fixing or mounting parts and even for pressure.
Hexagonal head with pivot
This screw, besides allowing connections with great tightening, offers the possibility to immobilize the union using a pin in the pivot.
Hexagonal head with flange
This type of screw also allows a great tightening. But its advantage is that it is not necessary to use a washer between your head and the piece to be joined.
With hexagonal head with pointed end (captive screw)
It is a rod that is twisted by one or two of its ends. It is known as a captive screw, because it prevents movement between the joined pieces, since it is placed between the nut and the screw. It is used for assembly.
Grooved and slotted head (phillips)
These screws are used when large tightening is not required. They have a straight groove on the surface of their head that is cut perpendicularly. In this case, flat head screwdrivers are required. Both allow to hide the head of the screw as long as a countersink is made to the entrance hole of the piece.
Like hexagonal head screws, this type of screw is also used in cases where you need to apply a large tightening as in securing cutting tools.
Cylindrical head with inner hexagon
Also called Allen, these screws have a hexagonal recess in the head to fit an Allen wrench. They are cylindrical pieces that are used in unions where great squeezes are needed and that they are also narrow.
This type of screws is used for joints that do not require a large tightening. In addition, they are often subjected to frequent manual assembling and dismantling.
This type of screw has a spherical head and a flat base.
Head of tallow drop
This is a screw that has a bearing surface with a conical shape and a slightly oval head.
It is a screw with a hollow in the head that has a star shape.
According to their material
They are one of the most common screws. The advantage of these is that they are lighter than steel ones. This quality makes the aluminum screws ideal for working with plastic or wood surfaces.
This is a variety of aluminum screws. In addition to being made with this component, they are also combined with other metals such as chromium, which makes their durability increase.
This type of screws are ideal for outdoor projects. In this case, parts that are capable of withstanding any environmental condition are needed. And stainless steel can withstand very wet conditions without deteriorating because they do not rust.
Plastic screws are ideal for those who require screw parts that can withstand different external conditions such as moisture and liquids. This type of screws are special for plumbing, for example.
The screws of this material are specially designed for jobs involving wood. And, in addition to being very resistant, they are aesthetically more appropriate than any other screw thanks to which they offer decorative touches.
According to your finish
These screws have a silver appearance. When cadmium is oxidized, it does not produce bulky corrosion products such as zinc. And this helps them to be used in closed tolerance functions.
It is a screw with a finish that is a metal zinc deposit. It has a semi-gloss appearance and is often used to protect steel from corrosion. It is recommended for use in industrial environments, because when used in humid environments, a white powder of corrosion is created that can interfere with the movement.
The appearance of this screw is iridescent yellow. This finish is achieved by the application of zinc (galvanized) and a later chrome. In this way, the resistance of the part against corrosion is increased.
It has a shiny metallic finish and its function is to protect the base metal from the screw. This finish also allows to increase the brightness of the piece. This type of screw is usually used to give decorative finishes.
This type of screw is also used for decorative purposes thanks to its shiny metallic appearance. The purpose of this finish, as in all other cases, is to protect the parts from corrosion.
It is a protective layer consisting of the immersion of the screws in a solution containing phosphoric acid. They are grayish-black in color.
These screws are semi-gloss and have an intense black color. They are so because they are subjected to a controlled oxidation of the steel, which is the one that produces this black layer that makes them resistant to corrosion.
According to its function
Self-tapping and self-drilling screws for sheet metal and hardwood
What characterizes self-tapping and self-drilling screws is that both pieces are able to open their own way.
Self-tapping has an end that has a conical shape. They can be flat-headed, rounded, oval or flat. In this type of screws the thread is thin and has a flat bottom so that the iron can be housed in it. They allow to join metal with metal, metal with wood, metal with plastic, among others. The edges of these pieces are sharper than that of the wood screws.
As for the self-drilling screws, they have a tip that is a drill bit. Which means that with them it is not necessary to drill guides to use them. They are often used with heavier metals.
Screws with thread for wood
Also called wood lag screws, they have a thread that occupies 3/4 of the tang. They are characterized by narrowing at the tip to open the way as they are inserted, this to facilitate the autoroscado. To use this type of screws it is not necessary to make a previous hole. They are usually screwed with a screwdriver, either manual or electric. In this case, the head type may vary.
- Flat : Used when the screw head needs to be submerged or flush with the surface.
- Round : It is used to join pieces that by their thinness do not allow the screw to sink. But it is also used to fix parts that need washers. It is a type of screw easy to remove.
- Oval : Are used to join metallic elements. And thanks to the shape of the head, allows it to sink into the surface and that only protruding the top that is rounded. They are also easy to remove and aesthetically look better than flat head.
Screws for metal joints
It is a type of screw that is used to fix metal parts. They have a triangular thread and can be screwed into a nut with washer in a through hole or in a blind hole.
These screws are usually used to fix parts of different machines. In these cases you need parts that are strong enough to withstand the stress to which the machine is subjected. They must be fully tightened so that they do not loosen during operation.
Wall and Wood Screws
This type of screws have a greater thickness than the classic screws for wood. These screws are often used to screw heavy element supports, especially those used to hang things on the walls of buildings such as air conditioners, among others.
To use this type of screws the wall must be drilled depending on the diameter of the screw that has been chosen. Afterwards a plastic wad is inserted and the piece is screwed.
According to its utility
It is a type of screw that is used to join two pieces. This connection is made through a through hole that does not have a thread, while being threaded in the other, as if a nut were involved.
It is a screw that is used to traverse the pieces to be joined. Do not thread in any of them. They are usually used for castings or for light alloys.
This screw is a threaded rod at both ends that has no diameter variation. In this case, the pieces are threaded. One is the one that is in charge of threading, while the other piece has external thread. The fastening is done with the use of a nut.
This is a type of safety screw that once it has been screwed, it is impossible to remove. The only way to do this is by forcing the piece until it breaks. This is achieved by having a design with a head tilted in the interior.
Which means that when trying to loosen it, the key will come out but not able to remove the screw. Because of their functionality, they are used in jobs located in public places where many people have access.
This type of screw is characterized by high tensile and fatigue resistance. They are often used when machines are constantly exposed to pressures, speeds and stress, as these processes need stronger joints to avoid failures.
Today electronic components tend to be smaller and smaller. For this reason, it has become necessary to create almost minute screws. These pieces are characterized by being self-tapping type and made of soft materials such as plastics. In addition, its head must be adapted so that it can be used with small and precision screwdrivers.
These are bolts whose diameter of the hole is usually 1 millimeter larger (approximately) than that of the stem of the piece. When joining with this type of screws requires a lower adjustment between the diameter of the piece and the drill to be used.
The calibrated screws differ from the ordinary ones because of their geometrical characteristics. As stated, in ordinary screws the diameter of the hole must be 1 millimeter larger than that of the rod. But in the case of the calibrated, both diameters are almost the same size. Therefore, they are usually used for precision joints and for the formation of rigid knots.
High strength screws
What distinguishes high strength screws from others is that the characteristics of the steel used to manufacture them must be standardized. That is why the manufacturers of these screws must, by obligation, deliver a certificate of guarantee. This type of parts must carry on the head both the letters TR and the designation of the steel type and the registered trademark of the manufacturer.
- Zavala, G. (1985). Thread: Screw. Autonomous University of Nuevo León. Mexico. Web: eprints.uanl.mx.
- Ramirez, W. (2013). Screws and bolts. Alas Peruanas University. Peru. Web: documents.mx.
- Valdez, C. (2015). Types of screws and their functions. Web: prezi.com.