What is a Bolt? – Types and Uses

What is a Bolt?

A bolt is a mechanical fastener with a threaded shaft. Bolts are closely related to screws, which are also mechanical fasteners with threaded shafts. These types of fasteners are typically inserted through two parts, with aligned holes.

According to some definitions, whether something is a bolt or a screw depends on how it is used. A bolt is inserted through parts which all have unthreaded holes and a nut is then screwed onto the bolt to provide a clamping force and prevent axial movement.

A screw may first pass through a first part with a clearance hole but its threads mate with threads in one of the parts being fastened. A screw may cut its own threads or mate with a threaded part.

In practice this definition is rarely used. The term bolt is usually used for a fastener which has only part of its shaft threaded. Fasteners with their entire shaft threaded are normally called screws. The unthreaded part of a bolts shaft is called the shank. The shaft of the bolt prevents radial movement of the parts, while the head of the bolt and the nut, if fitted, prevents axial movement.

The unthreaded shank provides an interface with the parts that is more precise and less abrasive. The shank also does not contain stress concentrations that could lead to failure, it is therefore important that the shank extends well beyond the interface between parts if a significant shear force will be placed on the bolt.

A bolt fastening a part to another part with a threaded hole, technically in this application it is acting as a screw.

Bolts often rely on axial force causing sufficient friction at the threads to remain in place. A torque is applied to the head to generate this axial force. The force acts between the bolt head and whatever the bolt is screwed into, whether that is a nut or one of the parts being fastened.

This causes elongation of the bolt and compression of the parts containing clearance holes. Alternatively, some form of locking nut or thread-locking adhesive may be used to prevent the bolt from loosening.

Parts of Bolt

Parts of Bolt

As shown in above Different parts of bolt describe as following.

  1. Head: It is the part of a bolt from where a spanner can hold it (to make it tight or loose).
  2. Shank: A bolt can broadly divide into two parts head and shank. Shank is partially threaded (as shown in the figure) to accommodate a nut.
  3. Grip length: It is the part of bolt that accommodates the parts which are to assemble. Grip length should be equal to the combined thickness of the joining parts.
  4. Thread length: It is the part of bolt that accommodates the nut.
  5. Nominal length: It is the sum of thread length and grip length (as shown in figure).

Type of bolt heads

Following are some most common types of bolt heads

  • Flat bolt head: A counter shank head with a flat top.
  • Oval bolt head: A counter shank head with rounded head top.
  • Pan bolt head: A slightly rounded head with a short vertical side.
  • Truss bolt head: An extra-wide head with a rounded top.
  • Round bolt head: A Dome’s head.
  • Hex bolt head: A hexagonal head.
  • Hex washer bolt head: A Hexagonal head with a round washer at the bottom.
  • Slotted hex washer bolt head: A hexagonal head with a built-in washer and slot.
  • Socket cap bolt head: A small cylindrical head using a socket driver.
  • Button bolt head: A low-profile rounded head with a socket driver.

However, there are many similarities between bolts and screws, there are some differences too.

Difference between Bolt and Screws

You can find some differences between screws and bolts fasteners, by looking at the figures above. Below are some other differences.

Bolt and Screw

According to a thesaurus, the difference is that there is no difference because the bolt fasteners and the screw are synonymous with each other. While it would be easy to do all of these determinations simultaneously. There are actually significant differences that a user needs to be aware of before making a purchase.

It is true that, to the naked eye, there does not appear to be much difference between the bolt and the screw. They are both threaded fixings and have a head for tightening the fastener, but more than that.

The most obvious way to distinguish between a bolt and a screw is that a bolt is usually not threaded all the way along its leg because it consists of a plain part. A screw, however, is completely threaded over the head.


A screw is usually installed in a tapped hole unless it is a self-tapping screw that forms its own thread. The screws do not need a nut, as they are secured tightly into the hole with a screwdriver or driver bit that fits into the drive recess. Typically, the screws are less than the width of the material they are screwing, so that they do not protrude on the other side.


The bolt is designed to be installed with a suitable nut. The hole for the bolt is not taped as the bolt is pushed and stabilized and tightened using a nut behind the material. So a bolt would be longer than the width of the material that is being used on it, as it would have to be spread from the other side to screw in the nut.

The unread portion of the bolt adds strength, making it more resistant to shear forces than fully threaded screws. The bolt is usually fastened using a spanner or other tool that holds the head while the nut is tightened.

Bolts can be used in the same way as screws if they are installed in threaded components.

Fully threaded bolts are also available.

Types of bolts

Following are some most common types of bolts

  1. Anchor bolt – The Anchor bolts are bolts design to attach a structural member or component to a concrete slab or PEED foundation. Anchor bolts can pre-set in place while the concrete structure is more, as with a plate used on top of the ground foundation of a house. Or, the anchor can attach after being cured using a drilling operation to create a channel into which an anchor bolt can be inserted.
  2. Blind bolt – Blind bolt refers to a style of the bolt that allows the use of a fastener in cases where the application does not allow tightening of the bolt or access to torque to both sides of the bolt. A simple example of this is the common toggle bolts use to secure objects to a wall at a location between the supporting beams.
  3. Carriage bolt – Carriage bolts are a form of a self-locking bolt that increases the level of protection by using a flush-mount dome head, which allows access only to remove or loosen these bolts from the nut’s nut side. Under the domed head of the bolt is a square section that can insert into a uniform square cut to provide a self-locking feature that allows the bolt to tightened from the side of the nut without the need to tighten it.
  4. Arbor Bolt – The bolt permanently attaches to the washer and the threading reversed. The Matter design for use in saws and other means to harden the auto during use to prevent blades from falling.
  5. Lift Bolt – Bolt with a large flat head used in conveyor system setup.
  6. Hanger Bolt – The bolt that has no head, has a machine threaded body followed by a wood threaded screw tip. Allow the nuts to attach to actually be a screw.
  7. J bolt – bolt-shaped bolt j. Used for tie-down. Only the non-curve section threaded to attach a nut.
  8. Lag Bolt – Also known as lag screw. Not a true bolt. Hex bolt head with thread screw tip for use in wood.
  9. Rock bolt – used in tunnel construction to stabilize walls.
  10. Sex Bolt or Chicago Bolt – Bolt consisting of a male and female part with internal threads and a bolt head. Commonly used in the binding paper.
  11. Double-end bolt – Double-end bolts are sometimes called stud bolts and without conventional heads have a threaded part at each end of the bolt. One end design to threaded into a suitable hole that is tapped with a mate, and the other end threaded to support the nut. The appearance is similar to a threaded rod, but is not traditionally threaded over the entire length of the stud and can be threaded separately at each end.
  12. Eyebolt – The eye bolt has a fully closed or partially closed-looped end in place of the conventional bolt head. The loop can in some cases use to lift the object to which the eyebolt is attached. Some eye bolts are not designate for lifting but may use to route wires, cables, or other similar elements to avoid accidental interference. Eyebolts may offer additional capabilities depending on material structure and finish – some are suitable for low-temperature operation while others design to not reflect light and will therefore blend into the background.
  13. Hex bolt– Hex bolts, also known as hexagon head bolts, are a very common form of bolt available in standard dimensional inches and metric sizes. As the name itself suggests, these bolts have a hexagon-shaped head suitable for tightening with a wrench or socket. Hex bolts can fully thread or show an unread shoulder.
  14. Machine bolt– Machine bolts use to fasten two pieces of material together, and are similar to hex bolts, except that they will not have a chamber point and design with a washer-bearing surface under the head has gone. They are usually available in both hex head and square head options.
  15. Penta-head bolts– Penta-head bolts are an example of a tamper-resistant bolt, which can use in applications where it is desired to reduce the likelihood that a person equipped with standard equipment may loosen or remove the bolt. With bolt heads in the shape of a pentagon, standard wrench or socket sets will be unable to be used on these bolts.
  16. Roundhead bolt- Similar to carriage bolts, the round head bolt does not have a square taper under the domed head of the bolt and is typically used to attach to the wood. The soft nature of the wood allows the bolt to compress against the surface of the wood and grip by friction to prevent the bolt from turning when the nut tightened.
  17. Shoulder bolt– The shoulder bolt, also called a stripper bolt, is a threaded bolt section of smaller diameter than the shoulder of the bolt (the part of the bolt between the head and the beginning of the threaded part). Shoulder bolts are useful to act as a shaft or axle that may include a rotating part, such as a bearing or bushing.
  18. Socket head bolt– A socket head bolt, also known as a socket head screw, uses a recessed head.

Selection of Bolts Material

Following materials are generally use for manufacturing the bolts:

  • Nylon Bolts: They are lightweight and water-resistant
  • Bronze and Brass Bolts: They are water-resistant
  • Stainless Steel Bolts: They have good strength and are corrosion resistant
  • Steel Bolts: They have good strength
  • Titanium Bolts: They are strong, light, and corrosion resistant
  • Plastic Bolts: They are inexpensive and corrosion-resistant. They are generally used for light loads.
  • Copper alloy Bolts: They are wearing resistant and have good load capacity.
  • Aluminum Bolts– They are thermally and electrically conductive. They are light and easy to manufacture. Apart from the above material, sometimes finishing material is also applicable to the bolts. The finishing material provides durability and corrosion resistance to the bolt. Here are some finishing materials used for bolts.
  • Zinc: Its coating acts as a sacrificial anode, protecting the underlying metal. It applies as fine white dust.
  • Black oxide– Its coating mostly uses for aesthetic purposes. It does not enlarge the dimensions of the bolt. It processes black rust.
  • Chrome: Its coating gives a bright, reflective finish. It is decorative and very durable. It applies by electroplating.

Manufacturing of Bolt

There are three major steps in the manufacturing a bolt:

  • Heading
  • Thread rolling
  • Coating

Bolts are normally made from wire. The wire is then cut to the proper length for the type of bolt being made. Heading produces the head of the bolt. The shape of the die in the machine dictates the features to pressed into the bolt head, for example, a round head bolt uses a round die. The threads are generally produced via thread rolling. However, some machined.

Finally, a coating, such as electroplating with zinc or black oxide, applied to prevent corrosion.

What is a Bolt Uses for?

Bolt uses in the following conditions when:

  • The parts that are fastened, require frequent dismantling and reassembly.
  • When the parts that are fastened, are made of a material which is too weak to make durable threads.
  • The parts that are fastened have medium thickness. For example, beams, flanges or plates, etc.
  • When there is a place available for bolt head and nut.
  • There is a place available for a spanner.

Relative advantages and disadvantages of screws and bolts fastener

  • Screws are cheaper compared 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.


What is a bolt?

A bolt is a mechanical fastener with a threaded shaft. Bolts are closely related to screws, which are also mechanical fasteners with threaded shafts. These types of fasteners are typically inserted through two parts, with aligned holes.

What are the types of bolts?

The principal types of bolts commonly used include:

Anchor Bolts.
Blind Bolts.
Carriage Bolts.
Double End Bolts.
Eye Bolts.
Hex Bolts.
Machine Bolts.
Penta-Head Bolts.

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