What is a Screw?

A screw and bolt are similar types of fasteners, typically made of metal and characterized by a helical ridge called a male (external) thread. Screws and bolts are used to fasten materials by engaging the screw thread with a similar internal thread (internal thread) in the matching part.

Screws are often self-threading (also known as self-tapping), whereas the screw is turned, the threads cut into the material, creating an internal thread that helps pull fastened materials together and prevent pullout. There are many screws for a variety of materials; Materials commonly fastened with screws include wood, sheet metal, and plastic.

A screw is a combination of simple machinery: it is essentially an inclined plane wrapped around a central shaft, but the inclined plane (threads) also run around the outside to a sharp edge that acts like a wedge as it is pushed into the fastened Material, shaft and helix also form a wedge at the tip.

Some screw threads are designed to mate with a complementary thread called an internal (internal) thread, often in the form of a parent object with an internal thread. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common use of screws is to hold things together and position items.

A screw usually has a head on one end that allows it to be turned with a tool. Common tools for driving screws include a screwdriver and wrench. The head is usually larger than the body of the screw, preventing the screw from being driven deeper than the length of the screw and providing a bearing surface.

There are exceptions. A carriage bolt has a domed head that is not intended to be driven in. A set screw may have a head equal to or smaller than the outside diameter of the screw threads; A grub screw is also sometimes referred to as a grub screw. A J-bolt has a J-shaped head that is sunk into concrete to serve as an anchor bolt.

The cylindrical part of the screw from the bottom of the head to the tip is called the shank; it may be fully or partially threaded. The distance between each thread is called the pitch.

Most screws and bolts are tightened clockwise, which is known as right-hand threads. Screws with a left-hand thread are used in exceptional cases, such as when the screw is subjected to counter-clockwise torque that would cause a right-hand screw to loosen. For this reason, the left pedal on a bicycle has a left-hand thread.

Parts of Screw

The three basic parts of a screw are the head, threaded shank and point.

Screw Drive: This is the slot your screwdriver tip will fit into. It is also known as the screw head. There are many such options; Accordingly, you should have a large number of screwdriver tips in your toolbox. There are many different designs of drives, but the three most common are Schlitz, Philips, and Pozidriv.
Screw Head: The head is the tip of the screw. It is usually wider than the shank and thread. Heads can be flat or domed. Some are small in diameter in relation to the shank and others are very wide.
Screw Thread: Amazingly, the thread has many components and varies between screws. There is the thread angle, which indicates how steeply it angles down. There is also spacing between threads that makes a difference. This is the pitch. Some screws have threads that are small and close together. Other screws have larger threads that are further apart.
Thread length: The thread length is either full length or partial length. Accordingly, there are fully threaded and partially threaded screws.
Screw Shank: The shank is the portion of the screw from underneath its head to where the threads begin.
Screw Tip: At the very end of the screw is the tip that penetrates the material first when the screw is being driven in. There are many different types of tips. The one on the left is specially designed for decking and therefore has a very sharp point.

What are screws made of?

Typically, screws and bolts are made from steel due to their strength and relatively inexpensive cost. However, screws and fasteners can also be produced from stainless steel, brass, titanium, and a wide range of other metals depending on the intended application.

The following material can use in the manufacturing of screws:

Titanium: Screws made of Titanium are hard, strong, light, and corrosion-resistant. When alloyed with other materials it can increase strength and durability.
Stainless steel: Screws made from stainless steel are chemical and corrosion-resistant. They have an appealing surface finish. They cannot harden like carbon steel.
Hardened steel: Screws made from hardened steel are hard but brittle in nature.
Steel: Screws make from steel are strong but they are vulnerable to corrosion.
Plastic: Screws made from plastic are inexpensive and corrosion-resistant. They use for light loads. They commonly use near water, such as water pools.
Molybdenum: Screws made from Molybdenum have a very high melting point and are exceptionally strong.
Copper alloy: Screws make from copper alloy have good load capacity and are wear-resistant. They are suitable for use near magnets.
Brass: Screws made of Brass are strong, conductive, and corrosion-resistant. They have low magnetic permeability.
Aluminum: Screws make of Aluminum are light and easy to manufacture. They are thermally and electrically conductive. They are resistant to corrosion.
Superalloys: Screws made of superalloys show good mechanical strength, surface stability, corrosion resistance, and resistance to creep at higher temperatures.

Apart from the above material, sometimes some finishing material is used in screws. It can provide durability and corrosion resistance to the screw. Here are some finishing materials used in screws.

Zinc: Its coating acts as a sacrificial anode, protecting the underlying metal. It is applied as fine white dust.
Chrome: Its coating gives a bright, reflective finish. It is decorative and very durable. It is applied by electroplating.
Black oxide: Its coating is mostly used for aesthetic purposes. It does not enlarge the dimensions of the screw. It processes black rust.

What about coatings?

Screws are often coated to make them even better by giving them desirable properties. Screw coatings open up a multitude of possibilities when it comes to finding the right fastener for a specific situation. For example, screws can be plated with copper, ceramic, zinc, and other materials that can provide added strength, added corrosion protection, or even an aesthetic quality that may otherwise be lacking.

For example, a galvanized steel screw fights corrosion better than a steel screw alone. Likewise, a copper-plated screw can look more attractive in a prominent place than a steel screw.

Manufacturing process of screws

There are three major steps in manufacturing a screw.

Heading
Thread rolling
Coating

The screw is usually made from the wire. The wire is then cut to the proper length for the type of screw being made. Heading produces the head of the screw. The shape of the die in the machine dictates the features to press into the screw head, for example, a round head screw uses a round die.

The threads are usually produced via thread rolling. However, some are a machine. Finally, a coating, such as electroplating with zinc or black oxide, is applied to prevent corrosion.

Uses of Screw

Screws are widely used in threaded fasteners to hold objects together and in devices such as screw tops for containers, vises, screw jacks, and screw presses.

Uses of screw-in following conditions:

When the parts that join, are thick enough to accommodate the threaded hole.
Bolts are good for frequent dismantling and reassembling, unlike screws.
Relative advantages and disadvantages of screws and bolts.
When the parts that are attached, that have sufficient strength to accommodate durable threads.
These use when the parts sometimes dismantle.
There is no place to accommodate the nut.
Screws are cheaper compare to bolts.
Bolts carry the load on a larger shank area when compared to the screw

Advantages and Disadvantages of screw and bolt

Screws are cheaper compare to bolts.
Bolts are good for frequent dismantling and reassembling, unlike screws.
Bolts carry the load on a larger shank area when compared to the screw.

References:

What is Screw?: https://en.wikipedia.org/wiki/Screw
Parts of a Screw: https://www.homestratosphere.com/parts-of-screw/

What is a Screw? – Different Parts of the Screw