Bolt | Types, Parts, Manufacturing, Material Selection, Applications

A bolt is a type of threaded fastener (like a screw) and is a male part. It is generally made of a metal. It is used to keep two or more hardware parts together (in a specific position).

Shank of the bolt is only partially threaded, just to accommodate a nut.

A bolt is sometimes also known as through bolt.

Note: Those who don’t know ‘shank’. It is discussed later in this article.

Note: Those who don’t know ‘What is a fastener?’. A fastener is a hardware device which mechanically affixes or joins two or more parts together.

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

Differences between screws and bolts

 

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

• A screw can have a tapered shank but a bolt can’t because it has to be assembled with a nut
• Bolt require nut to have a grip on the joining parts but screw doesn’t.
• Bolts are used to assemble two non-threaded parts together (unlike screw).
• Screws are smaller in size when compared to bolts.
• Screws have a large variety of head whereas bolts have either hexagonal or square head.

Parts on bolt

As shown in above diagram a bolt can be divided into following parts.

• Head: It is the part of a bolt from where a spanner can hold it (to make it tight or loose).
• Shank: A bolt can be broadly divided into two parts head and shank. Shank is partially threaded (as shown in figure) to accommodate a nut.
• Grip length: It is the part of bolt that accommodates the parts which are to be assembled. Grip length should be equal to the combined thickness of joining parts.
• Thread length: It is the part of bolt that accommodates the nut.
• 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

• Hexagon flange head
• Hexagon (trimmed) head
• Indented hexagon washer head
• Indented hexagon head
• Square shoulder head

Types of bolts

Following are some most common types of bolts

• U-Bolt
• Shoulder bolt or Stripper bolt
• Sex bolt or Chicago Bolt
• Rock bolt
• Lag bolt
• J bolt
• Hex bolt
• Hanger bolt
• Elevator bolt
• Carriage bolt
• Arbor bolt
• Anchor bolt
• Flange bolt
• Machine bolt
• Plow bolt
• Square head bolt
• Stud bolt
• Timber bolt
• T-head bolt
• Toggle bolt

Selection of bolt material

Following materials are generally used 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 wear resistant and have good load capacity.
• Aluminium Bolts: They are thermally and electrically conductive. They are light and easy to manufacture.

Apart from above material, sometimes finishing material is also applied to the bolts. 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 is applied as fine white dust.
• Black oxide: Its coating is mostly used for aesthetic purpose. It does not enlarge the dimensions of the bolt. It is a processed black rust.
• Chrome: Its coating gives a bright, reflective finish. It is decorative and very durable. It is applied by electroplating.

Manufacturing of Bolts

There are three major steps in the manufacturing a bolt.

1. Heading
2. Thread rolling
3. 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 be 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 are machined.

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

Applications of Bolt (or Through Bolt)

Bolt can be used in following conditions

• When the parts that are fastened, require frequent dismantling and reassembly.
• When the parts that are fastened, are made of material which is too weak to make durable threads.
• When 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.
• When there is a place available for spanner.

Relative advantages and disadvantages of screws and bolts

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

Images sources:

Bolted Joint: By Yuri Raysper – Has drawn from the bookThis W3C-unspecified vector image was created with Inkscape., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1761128

Screw Joint: By Yuri Raysper – Has drawn from the bookThis W3C-unspecified vector image was created with Inkscape., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1761139

Parts of Bolt: By Mikael Häggström – Own workAnnotations: W. E. Johns. Notes on Nuts and Bolts. gizmology.net. Copyright note from 2003Source image:Public Domain, CC0, https://commons.wikimedia.org/w/index.php?curid=77327491