What are Shoulder Bolts?

A shoulder bolt is one of the many machine screws used for construction and household items. It has an unthreaded shoulder below the head that is larger than its threads. Shoulder bolts, also known as shoulder screws, are unique and can be customized in different sizes and materials.

This is a close look at a row of shoulder bolts.

Did you know there are various kinds of bolts? I didn’t. I thought when you bought bolts, there was only one kind. You just needed to find the right size you needed for the project. Whether you’re putting together a bed, a bookshelf, or a deck, you’re probably going to need some bolts.

However, which bolts you will use depends on what you’re building because there are many different kinds of bolts. There are anchor bolts, elevator bolts, hex bolts, shoulder bolts, and more. The different bolts look differently, and their shape and head type characterize them. They also are used for different projects.

For instance, an anchor bolt attaches objects to concrete, while hex bolts are useful in engineering, the auto industry, and construction. They are so named because the head of each bolt has six sides, like a hexagon. Although there are many different kinds of bolts, we are going to be talking about shoulder bolts.

Related: All Types of Bolts

What Are Shoulder Bolts?

A shoulder bolt, also known as a shoulder screw, is a machine screw with a nonthreaded shoulder, which lies below the head, larger in diameter than the threads themselves. Like other screws, shoulder bolts’ purpose is to hold objects together and keep objects in an uncertain position.

They don’t have a tapered shank, so they are unable to self-thread into soft material. They can come in commercial grade and precision grade. Commercial grade bolts used to be the industry standard but are now being replaced by precision grade because they have tighter diameter and length tolerances than a commercial grade.

The tighter tolerances make them ideal for use with ball bearings and other precision components. A precision shoulder screw can also provide more flexibility when looking for the right one you may need for your application. Engineers can choose the head type, shoulder and thread size, and other variables to fit their specific applications.

Sections Of A Shoulder Bolt

Shoulder bolts have three main sections. These sections are the cylindrical head, smooth cylindrical shoulder, and the thread.

  • The head diameter is larger than the rest of the body.
  • Its diagram and length describe the shoulder.
  • The thread length has a diameter that is slightly smaller than the shoulder.

Shoulder bolts come in a variety of diameters and lengths. However, the shoulder is what determines the size of the screw. The overall length of a bolt is calculated by adding the head’s height, length of the shoulder, and length of the threaded portion. When looking for the size of bolts you need in a store, the description will be by their diameter and length. For example, 3/8 x 2 bolts have a diameter of 3/8 inches and a length of 2 inches.

This is a close look at a copper cable held in place by shoulder bolts.

What Are The Functions of Shoulder Bolts?

Shoulder bolts are used in applications for industries, from aerospace to consumer products. They are versatile and have unique attributes when installed. When the shoulder screw thread is fully installed, like in a wall or piece of wood, the unthreaded shoulder part will sit outside the surface. Its installation allows it to act as a shaft or dowel for rotating items like bore and bushings. The shoulder of the bolt is what gives the bolt its versatility. They can act as:

  • Axle for rolling parts
  • Guides for sliding elements
  • A pivot point or mounting pin

Other uses include using them in punch and die mechanisms where the bolts act as straight slides to accurately align the mold’s halves as they open or close. Another use is attaching a socket stripper plate, giving them the name stripper bolt.

What makes the shoulder bolts unique is the different types of mechanical assembly components the shoulders can accommodate. Bearings mounted on shoulders can rotate at moderate speeds on pulleys, gears, and sprockets.

Shoulder-mounted springs can preload components traveling along the length of the shoulder. On different applications, the shoulder bolts can act as shafts for cam rollers and bearing pins for swing arms, links, and levers. When combined with bronze sleeve bearings, they can be used as a guide in blanking and forming presses.

Another thing to keep in mind is to make sure that the shoulder bolt is not over-torqued. If it is over-torqued, the bolt will most likely fracture. Properly torquing a socket shoulder screw will stretch it like a spring, thereby reducing the chances the bolt will come loose from outside forces.

What Materials Are Shoulder Bolts Made From?

The materials of shoulder bolts are dependent on what you are using the custom shoulder bolt for. The sturdier the material, the stronger the bolt will be. Materials used to make a bolt include:

  • Steel is the most common material used. It is used in many household projects and where weather will not affect the bolt from corrosion.
  • Stainless steel offers extra strength and protection than regular steel, as it is an alloy. Alloy steel has corrosion resistance, useful when the bolts are being used in different weather. It won’t lose its unique properties when scratched or damage and is often used in construction near water.
  • Bronze is another alloy and also contains copper and other metals. It is often used when products need to be waterproof, like in wooden boat construction.
  • Nylon is lighter and not as strong as other materials. It is used when the product needs to be waterproof, like home appliances and automotive parts.

Other materials often used to make bolts include plastics and brass, depending on the project and how sturdy the bolt must be.

A bunch of shoulder bolts.

Frequently Asked Questions

What is a standard bolt size?

As bolts vary in size or shape, the standard size varies by type and project. It all depends on what you need the bolt for as to what size you will use. Therefore, it’s hard to determine the standard bolt size because the standard size of a shoulder bolt may be different from the standard size of a hex head shoulder screw, and so on, because the bolts are different as the projects worked on.

How do you know if your bolts are standard or metric sizes?

It’s effortless to tell whether your bolts are measured in standard or metric. If the measurement is standard, it is measured in inches, and the sizes are specified by shoulder diameter and shoulder-length, followed by overall length. If the measurement is in metrics, the measurement will be in millimeters, and the sizes are specified by shoulder diameter, then thread diameter, then shoulder length.

How do you select the right shoulder screw for your application?

To select the right screw for your application, you will need to know what specifications are needed for the head, shoulder, threads, and material the screws will need to be made from. Think about the project you’re working on, and that will help determine the size and material of the shoulder screw needed.

Is a bolt a type of screw?

bolt is similar to a screw, yet they have differences. They share the same shape and are both used to fasten materials together. However, a bolt should be used with a fastener, like a nut, while a screw doesn’t need one. Another difference is the bolt isn’t threaded down the shank or body. In contrast, the screw is threaded entirely from the head down.

What’s the difference between a bolt and a cap screw?

The difference between a bolt and a cap screw is the way the fasteners are installed. You install a bolt by turning a nut to tighten it. A cap screw does not need a nut to tighten it. It is tightened by turning the head of the bolt.

A close look at various bolts, nuts and screws.

What are the types of bolts?

There are many different types of bolts. These bolts include:

  • anchor bolt
  • arbor bolt
  • carriage bolt
  • elevator bold
  • hanger bolt
  • hex bolt
  • j bolt
  • lag bolt
  • rock bolt
  • Chicago bolt
  • shoulder bolt
  • u-bolt

These are just a few of the different bolts. There are many more depending on what you need to use the bolt for.

Why do bolts have shanks?

The shank is the threadless part of the bolt between the head and the thread, often known as the body. The shank of the bolt can increase the shearing capacity or increase the elastic resiliency of the bolt. Shanks with larger areas increase the performance of the bolt in shear loading. In high-performance bolts, the shank can be reduced to the smallest possible to compensate for the increased rigidity, ensuring elasticity. Bolts should be more elastic when used as tension bolts.

What are the sizes of bolts?

The sizes of bolts can vary. Standard grade shoulder bolts can vary from 1/4 to 2 inches or 6 to 24 millimeters. Precision shoulder bolts can range from 3/32 to 1/2 inches and 6.5 to 12 millimeters in diameter.

How can you tell the size of a bolt?

To determine the bolt’s size, measure the head’s length to the end of the thread. Measuring the distance from the outer thread on one side from the outer thread on the other side can determine the diameter.

What is a hex bolt?

A hex bolt is one of the most common types of fasteners. It is often used as a standard bolt as you can use it for various things, including construction and home improvements. Their name comes from their shape as the bolt’s head has six sides, making it easier to grip with tools from any angle. You can even use your hands to twist the hex bolt. This bolt is used in buildings, bridges, docks, and highways.

What do you call a screw hole?

A screw hole is the hole created in the material when using a screw or a bolt.

How do you measure a shoulder screw?

Its shoulder diameter and shoulder-length measure a shoulder screw. The overall shoulder length is the head’s height plus the shoulder’s length plus the length of the threaded portion.

What is a vented screw, and why would you need one?

Vented screws are also called vacuum, ventilation, or hollow screws. These screws have a hole drilled through them and are specifically designed to release gases, contaminants, and pressure. They are often used within vacuum systems and allow for the quick evacuation of trapped pockets of air and other contaminants from the blind-tapped holes in different systems.

Blind-tapped holes leave a small void beneath the fastener, resulting in all particles and other contaminants to stay in place. Vented screws combat these issues by releasing the contaminants and preventing any leaks.

What does m8 1.25 mean?

M8 1.25 is the metric measurement of the bolt. It stands for 8 millimeters in diameter and 1.25 millimeters in length.

What is a Chicago bolt?

A Chicago bolt, also known as a sex bolt, has both male and female attached parts with internal threads and bolt heads on both ends. They are more commonly used for paper binding.

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