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.
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.
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 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
