Imagine a world where everything runs smoothly—machines work in perfect harmony. A big reason for that? Fasteners—especially bolts. These essential components help hold everything together, playing a crucial role in keeping structures and systems safe across countless industries.
Bolts are often available with a complementary nut and are equipped with threads. They differ depending on design, strength, threading, and material, enabling different types of bolts to serve unique roles.
Here’s a comprehensive guide covering the most common types of bolts and nuts and how to choose them.
Different types of bolts are effective in diverse scenarios depending on factors like material compatibility, environmental conditions, and load-bearing capacity. Choosing the right fastener among the different kinds of bolts influences the following:
The different parts of a bolt include:
Imagine trying to tighten a bolt with the wrong tool—it slips, strips the metal, and leaves you with a fastener that won’t budge. Frustrating, right? That’s why bolt drives matter. A bolt’s drive is the part that lets your tool “grab” and turn it. It’s what connects your wrench, screwdriver, or socket to the fastener and helps apply the torque needed to hold things together—or take them apart.
But here’s where things get tricky: drives, heads, and tools often get lumped together, even though they serve different purposes. Let’s break it down so you can choose the right fastener for the job—and avoid any stripped bolts or mismatched tools along the way
Here are some of the most common bolt drive types you’ll come across:
While the drive is about how the bolt is turned, the head is about how it sits against a surface and how force is distributed. The head shape also affects the bolt’s appearance, clearance, and function.
Here are a few common bolt head styles:
No matter how well-designed a bolt is, it won’t do much good without the right tool. Matching your bolt’s drive with the correct tool helps prevent stripping, improves efficiency, and makes your project go a whole lot smoother.
Here’s a lineup of tools matched to their respective drives:
This is the round section of the bolt that handles the shear forces acting on the bolt. It prevents lateral movements of the fastened parts. It comprises two key components:
This is the perfect partner for a bolted joint with or without a threaded hole. The nut provides the required clamping force to fasten different parts and prevent axial movements. It supplies a counteracting axial force that causes compression of the secured components. Some other ways of securing a bolted joint subjected to prolonged impacts and vibrations include using:
This is a thin, flat disc with a central cavity. You usually place it under the nut and bolt heads. It helps distribute the load of the threaded bolt over a wider area, preventing the fastened bolt from eroding or deforming the underlying material.
Washers, although typically made of metal, often comprise soft materials like urethane, rubber, and plastic. This choice of material can efficiently absorb vibrations and reduce the risk of the bolt thread unfastening. It can also provide a watertight seal, preventing liquids from entering the bolt joint.
If you’re in the market for an ideal fastener for use in residential, commercial, and industrial settings, then there’s a bolt type out there just right for you. Below, we’ll explore some of the most common types of fasteners and where they typically appear.
Also known as hex cap screws, these are among the most versatile types of threaded fasteners, comprising a six-sided or hexagonal bolt head. This design is easy to grip, allowing you to easily tighten or loosen it with standard tools like:
This bolt head variant is unslotted and can have threads running throughout the entire length. Owing to their exceptional strength and ease of use, hex bolts are commonplace in construction, machinery assembly, and home improvement projects. For more demanding structural applications, larger bolts can provide the added support needed for high-load environments.
This type of bolt is easily identifiable by its smooth, domed head and square neck beneath it. The square neck portion prevents the bolt from turning unintentionally when securing it in place. It is common in wood applications like furniture, playground equipment, and fences.
The domed-head design provides a clean, tamper-resistant surface that meets the wooden project’s aesthetic and safety requirements.
Lag bolts, also referred to as lag screws, are thick, heavy-duty fasteners with coarse threads and a pointed tip. They feature a square or hexagonal head and a threaded shank. The threads and shank are tapered to enable you to easily drive and secure the fastener through wood or masonry without a nut.
The threading generates friction between the secured materials, preventing slippage and strengthening the connection. Larger lag bolts are ideal for high-load applications like:
Notably, the lag bolts are more taxing to remove once installed and require careful planning when you intend to use them.
This U-shaped fastener features threads on both ends of each arm. The curved shape ensures a snug, secure fit around cylindrical components. At The Federal Group USA, we craft the U-bolts using various materials like:
The size of U-bolts depends on the distance between the arms and the overall length from end to end. U-bolts are commonplace in plumbing and HVAC systems. They help support the piping by guiding, resting, stabilizing, and holding pipes and tubing on flat surfaces. There are two common types of U-bolts:
This bolt type features a distinguishing circular, looped, or ring bolt head. The eye bolt may have a shoulder or lack one. The shoulder imparts better strength and support to the fastened component. This looped feature serves as an anchor point for ropes, hooks, and chains, which are found to be used in rigging, lifting, and hoisting equipment . Some of the variations of eye bolts you may encounter in the market include:
This bolt type has a curved end resembling the letter ‘J’ shape. It has threads at the opposite end of the curve. This curved shape provides two contact points for fastening components and also offers strong resistance against pull-out forces. In addition, it enables insertion into pre-drilled cavities.
J-bolts are ideal for anchoring different components to concrete bases, like:
You can install the J-bolt by embedding it into wet concrete or placing it into two pre-drilled holes. One cavity accommodates the threaded straight portion, while the other hole holds the flat end of the ”J.” J-bolts are common in parks and gardens, where they secure playground equipment and benches to concrete surfaces.
This special bolt type serves to attach structural elements to concrete foundations. It exists in the following two forms:
The anchor bolt you choose for fastening the base plate and street signage to concrete foundations can be :
Shoulder bolts or stripper bolts uniquely feature a smooth, cylindrical shoulder between the threaded end and the head. This shoulder has a significantly wider diameter than the threaded section, but is still smaller than the bolt head.
The shoulder provides a bearing surface or pivot point in machinery. It is common in assemblies that experience constant vibrations or heavy loads, such as:
When fully installed, the smooth shoulder extends beyond the threads, providing a shaft for rotating components like
Named for its use in conveyor systems and elevator construction, this bolt variant features a large, flat, thin, countersunk head. Its threads extend through a majority of the shafts. After securing the elevator bolt properly, it should sit flush with the surface. The wide, flush finish enables even weight distribution throughout the moving panels and belts. These snag-free surfaces are common in the agricultural industry and food processing machinery.
TC bolts are specialized fasteners commonly used in structural steel and the construction industry. They have a spline at the end that breaks off when the bolt is tightened with the right amount of tension. This feature guarantees consistent clamping force and eliminates guesswork. Typically cold forged, TC bolts are common in large-scale projects like bridge construction and high-rise buildings. In these scenarios, exact torque and uniform performance are key to structural integrity.
Beyond the common varieties, there are different kinds of bolts for very specific tasks.
This bolt type has an integral washer-like flange under the bolt head. The component spreads the load or clamping force across a wider area. It commonly secures the outer casing of the:
The design lowers surface pressure, limiting damage to the fastened material. It is also present in heavy machinery and construction equipment, where constant vibration can loosen joints.
This heavy-duty fastener features a convex, domed, or flat head with a tapered neck, along with a partially or fully threaded shank. Its neck is usually square but ends up tapering as it connects to the threads or shank. Its designers intended the bolts’ use in securing earth-moving machines like snowplows and bulldozers.
The bolt head has an 80-degree taper that allows soil or debris to pass over the bolt head smoothly.
Different types of bolt heads fit specific tools, torque requirements, and surface finishes. These are some of the most common bolt head shapes and their uses.
This bolt head features six flat sides that are easy to grip with everyday power tools.
This more traditional bolt head has a four-sided design style that predates the hex head. Its large flat sides are less likely to slip, allowing you to easily fasten them even in small, dim areas with restricted visibility.
In addition, the square shape resists rounding more effectively than hex heads, making them easier to grip, especially when working with worn or rusted bolts.
The head bolt shape sits flush on the material surface after fastening it completely with a Philips screwdriver or hex driver. It has a countersunk design, where the head tapers underneath and fits into a conical hole.
This bolt variant has a smooth, dome-shaped top that remains visible above the surface after installation. It imparts a polished final look and is ideal for light-duty applications like
Also known as Allen bolt or cap screw, this bolt head features a cylindrical head with an internal hex drive. The design allows you to tighten it with an Allen wrench or hex key to far greater torque standards than conventional bolt types.
Threads refer to the spiraled ridges on a bolt that engage with a nut or tapped hole to create a secure joint. The two most common types are:
These types of bolts have fewer threads per inch, meaning the threads are more widely spaced. The design enables:
This bolt variant has more threads per inch and offers the following perks:
However, the fine threads have cons, like increased susceptibility to damage from corrosion or dirt, and more need for careful alignment to prevent cross-threading. Apart from the difference in threads per inch, the bolts’ threads can also vary in terms of the direction of fastening. This gives rise to:
A bolt’s performance and longevity depend on the material type and surface coating. Some of the common bolt materials include:
For the protective coatings and finishes, you can find bolts that have undergone:
You may have noticed strange engravings on fastener heads when shopping for nuts and bolts. These markings by the tool manufacturer denote the bolt’s material, make, and dimensions. Three main governing bodies determine bolt grades and standards that you may come across. They include:
The ASTM A307 is the standard for fasteners, which has two main grades:
ISO 898-1 provides the standard for metric grades of bolts and screws. It includes 10 different property classes, with the most popular ones being:
For in-depth reference tables and technical standards, seasoned engineers often turn to resources like the Machinery’s Handbook.
There are several key factors to consider when selecting the right fastener for the job. They include:
Regular inspection and maintenance help ensure fastened components remain secure and functional over time. You can evaluate the different parts of a bolt periodically for signs of wear and discoloration, corrosion and rusting, and loosening. If bolts are worn or their threads are damaged, replace them to maintain the integrity of the connection.
Choosing the correct bolt for your next project promotes safety and guarantees longevity. This extensive guide to the different bolt types and selection tips lets you pick the best fastener grades for the job.
Consider partnering with an experienced custom fastener manufacturer like The Federal Group to ease the selection process. We produce reliable, customized bolts for numerous industries and use cases. Contact us today to discover how our exceptional fasteners can drive your next venture forward.
