Big Bolt | The Federal Group USA
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Big Bolt

Learn everything there is to know about large bolts to make sure you have the tools and knowledge you need to pick the right big bolt every time.

The significance of bolted joints, when compared to other components that comprise an assembly, is often taken for granted. Picking the right bolts are far more complex than simply picking ones that fit and mate two parts together.

TFG USA Big Bolt 1

Regretfully, there is sometimes a tendency to underestimate this complexity. When picking the right bolt, you also need to consider the diameter, length, thread pitch, material, and strength requirements.

For larger bolts, the complexity only grows.

Large bolts are typically used in more heavy-duty applications such as construction, highways, bridges, off-highway, or heavy machinery such as semi-trucks, heavy trucks, tractors, agricultural equipment, and construction vehicles.

Bolts are mechanical fasteners with an externally threaded shaft and are usually coupled with a matching internally threaded nut. A big bolt is simply a large bolt. Should a bolt fail in the above applications, it could come at the cost of human life. This makes picking the right big bolt all the more critical.

TFG USA Big Bolt 2

How big is a big bolt?

While most people may be familiar with smaller, standard-sized bolts and screws (i.e. up to M10 for metric bolts and 7/16” for inch size bolts), bolts can actually be larger. Much larger. 

A big bolt is typically any bolt that is equal to or larger than M16. Bolt sizes can be as large as M100 or about 4” in diameter! 

With more specialized and advanced manufacturing methods available today, practically any size of bolt can be made. If there is a need for a custom big bolt, we can produce it.

A big job calls for a big bolt

Big bolt products

Most people will have used smaller, standard-sized bolts whether for furniture assembly, home improvement, or any other type of project. Bolts are used with a nut or can be threaded directly into a tapped (threaded) hole. Below are products in which big bolts are often used:

  • Turbine bases
  • Bolts for gear cases and generators
  • Tower constructions
  • Bolts for wind turbine blades
  • Cranes
  • Truck suspension
  • Pumps and valves
  • Water pipelines
  • Earth movers
  • Bulldozers
  • Large conveyors
  • Mining vehicles
  • Pressure vessels
  • Solar panels
  • Structural projects
  • Antenna towers
  • Bridges
  • Roller coasters

Big bolt industries

While smaller bolts are used in smaller assemblies, big bolts are used in more heavy-duty, high-load, and potentially risky settings. Some common industries in which large bolts are used are listed below:

  • Agricultural Equipment
  • Bridge Building
  • Highway Construction
  • Wind Farm/Wind Power
  • Sustainable Energy
  • Railways
  • Shipbuilding
  • Petrochemical
  • Oil & Gas
  • Heavy Truck
  • Waste Water Treatment
  • Sewage Treatment
  • Machine Building

If a big bolt were to fail in any of these applications, it could lead to a potentially destructive scenario and the devastating loss of life. The chance of something like this happening, no matter how slim, makes picking an appropriate big bolt vital.

How to pick the right big bolt

First and foremost, you should consult with a seasoned engineer. 

When choosing a big bolt, pick the one that fits into the holes (threaded or non-threaded) of the two parts that are being mated. However, it’s important to consider more aspects such as bolt material and bolt type, among other things. Here are four things to consider when shopping for a big bolt:

1. Size

It’s a no-brainer that a bolt’s job is to hold two parts together. What’s actually happening is that the bolt develops a clamping force within the joint that is strong enough to prevent the parts from separating. Therefore, simply matching a bolt and nut may not be sufficient to mate two parts together if there is not enough clamping force created. To pick the right big bolt, you need to:

  • Determine the type and direction of loads in the system.
  • Calculate the required clamping force of the joint.
  • Select the smallest bolt diameter able to support the clamping force.

It is advantageous to pick a big bolt with the smallest diameter that can support the load and with a long clamp length. A general rule of thumb is to have a bolt that is 1.5 times as long as its diameter. This not only helps reduce the loss of clamping force but also helps create an elastic joint that softens the impact vibrations can have on the bolt.

2. Bolt material and surface coating

A bolt’s susceptibility to corrosion is directly impacted by its material and coating. Should corrosion proliferate uncontrollably, it can compromise the strength of the joint. Some materials (like stainless steel and brass) are highly resistant to corrosion, while others (like plain carbon steel) are vulnerable to corrosion. Below are the materials used for big bolts:

  • Alloy
  • Carbon
  • Inconel 718
  • UNS S17400
  • Exotic Metals
  • High-tensile Steel
  • AMS 5643
  • ASTM A564
  • ASTM A693
  • Duplex
  • Waspaloy
  • Tantalum
  • Monel
  • Titanium
  • 17-4 PH
  • Molybdenum
  • A-286
  • Zeron
  • Stainless Steel
  • Multiphase Steels

While not all the materials above are inherently corrosion-resistant, corrosion resistance can be enhanced through various surface coatings where tiny layers of corrosion-resistant metals are added to the surface of a part by chemical processes. Notably, alloys and carbon steels are often surface treated. Surface coating of big bolts includes:

  • Hot-dip galvanizing
  • Zinc flake
  • Zinc plating
  • Chrome plating
  • Phosphate
  • PTFE

Picking the right material and coating for your big bolt will help ensure it will be able to withstand both the required loads and the environment it will be used in.

3. Bolt strength

Bolt material also directly impacts bolt strength. Some materials are inherently stronger than others and are more suitable for big bolt applications (e.g. steel bolts are stronger than brass bolts). Bolts are classified into “grades” which helps to identify their material and surface coating quickly. These grades have been characterized by standardization bodies such as ASTM or SAE. Grades of bolts are codified based on markings on their heads. US carbon steel bolts are classified as: 

  • Grade 2
  • Grade 5
  • Grade 8
  • Grade 9
  • Grade A325
  • Grade A-286

Metric carbon steel bolts are classified as:

  • Class  8.8
  • Class 10.9
  • Class 12.9

It’s important to pick a bolt grade and size that is sufficient to support the clamping force required by your specific project.

4. Bolt type

There are many different types of bolts. Depending on how parts are mated, one type of bolt may be more advantageous than another. For example, anchor bolts are used to secure large structural members to concrete. You wouldn’t want to use a shoulder bolt for this application since shoulder bolts are often used with rotating parts such as shafts and bearings. Here is a list of different bolt types:

  • Hex bolts
  • Heavy hex bolts
  • Square head bolts
  • Eye Bolts
  • Stud bolts
  • Flange bolts
  • Socket head bolts
  • Stripper bolts
  • Carriage bolts
  • Plow bolts
  • U bolts
  • Blade bolts
  • Round head bolts
  • Tower flange bolts
  • Anchor bolts
  • Foundation bolts
  • Structural bolts

The types of bolts listed above come in standard sizes. For big bolts, sizes can range from M30 to M100. When shopping for a big bolt, consider the application on which the bolt is to be used and select accordingly.


What is a fastener company?

A fastener company is a company that manufactures and sells a variety of fasteners. These include bolts, screws, nuts, rivets, and pins among other things. 

How is a big bolt manufactured?

Large bolts can be made from the following processes:

Hot/cold forging

In hot forging, molten metal is shaped into the desired fastener shape via a mold. Whereas cold forging molds metals into desired shapes at room temperature. Threads are then cut by roll forming or the cutting processes.

CNC machining

A big bolt can also be made by CNC milling and turning processes. CNC machining allows for precise large bolts that can be made with unique profiles and pitch diameter.

Cold forming

Similar to cold forging, cold forming does not require heating. Metal is struck or pressed into a die to make the desired shape. This is typically done through a series of extrusion processes that gradually moves material to obtain the required diameter. Roll forming is then typically used to cut the threads onto the shaft.

Big bolts are beneficial

It’s one thing to underestimate the complexity of selecting the right bolt for any project, but when the wrong big bolt is selected for more heavy-duty applications, it could come at the cost of human life. It’s important to consider the factors described above when shopping for a big bolt. 

Thankfully, our experts at The Federal Group are quite knowledgeable about bolts. Whether you’re designing a new product, working on a new project, or making modifications to an existing product, we can help.

Other big bolt suppliers can’t match the superior quality and exceptional customer service TFG provides. Contact a TFG sales representative today to discuss your bolt and big bolt needs.

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