What are Bolts and Nuts? Materials, Sizes, Types, How to Choose

Tristar Bolts and Nuts

What are Bolts and Nuts?

Bolts and nuts are hardware fasteners commonly used in construction, manufacturing, automotive, and various other industries. They are used to join two or more components together securely.

Bolts typically consist of a threaded shaft with a head at one end. The head may be hexagonal, square, or another shape, designed for a specific tool like a wrench or a socket. The threaded portion extends from the head to the tip.

On the other hand, nuts are a small metal block with a threaded hole in the center. They are designed to be paired with bolts. When a bolt is inserted through holes in two or more objects, a nut is screwed onto the threaded end of the bolt to hold the objects together.

When we talk about bolts and nuts, there are other hardware fasteners commonly used with them, namely screws and washers.

Washers are thin, flat discs which are used in conjunction with screws, bolts, or nuts to distribute the load of the fastener over a larger surface area and prevent damage to the surface being fastened. Washers also help prevent the loosening of the fastener over time by providing a smooth bearing surface and reducing friction.

Screws are similar to bolts but typically have a pointed tip and are designed to be inserted into a pre-drilled hole. Like bolts, screws have a threaded shaft and a head. Screws are commonly used in woodworking, metalworking, electronics, and many other applications.

What are Bolts and Nuts? Materials, Sizes, Types, How to Choose

How Do Bolts and Nuts Work?

Bolts and nuts are fasteners that work together to hold objects in place. A bolt is inserted through aligned holes in the objects, and a nut is threaded onto the bolt’s end. Tightening the nut secures the objects.

Materials of Bolts and Nuts

Bolts and nuts are available in various materials, each with its own characteristics and suitability for different applications. Here are some common materials used for bolts and nuts:

1. Steel

Carbon steel: Affordable and versatile, carbon steel bolts and nuts are widely used in many applications. They offer good strength and moderate corrosion resistance but may rust over time if not protected.

Stainless steel: Known for its excellent corrosion resistance, stainless steel bolts and nuts are suitable for applications where resistance to rust and corrosion is essential. They are often used in outdoor and marine environments.

2. Brass

Brass bolts and nuts are corrosion-resistant and have good electrical conductivity. They are commonly used in electrical and plumbing applications where conductivity and corrosion resistance are important.

3. Aluminum

Aluminum bolts and nuts are lightweight and have good corrosion resistance. They are often used in applications where weight is a concern or where corrosion resistance is required, such as in aerospace and marine industries.

4. Titanium

Titanium bolts and nuts are lightweight, strong, and highly corrosion-resistant. They are commonly used in aerospace, medical, and automotive applications where high strength-to-weight ratio and corrosion resistance are critical.

5. Copper

Copper bolts and nuts are known for their excellent electrical conductivity and corrosion resistance. They are often used in electrical applications and in environments where corrosion resistance is essential.

6. Plastics

Plastic bolts and nuts, such as those made from nylon or polyethylene, are lightweight, corrosion-resistant, and non-conductive. They are commonly used in applications where metal fasteners may cause corrosion or electrical conductivity issues, such as in electronics and plumbing.

When selecting the material for bolts and nuts, consider factors such as strength, corrosion resistance, conductivity, weight, and cost, as well as the specific requirements of your application. Choosing the right material will ensure that the bolts and nuts perform effectively and reliably in their intended environment.

Sizes of Bolts and Nuts

The sizes of bolts and nuts vary based on different standards and measurements. Here are some references to help understand the sizes of bolts and nuts:

Bolt Sizes

  • Bolt sizes are often specified using diameter and thread pitch dimensions in millimeters. For example, M8-1.0 x 20 indicates a bolt with an 8mm diameter, 1.0mm thread pitch, and 20mm length.
  • Metric bolts can have coarse, fine, or extra fine thread pitches. Coarse threads have more threads per inch compared to fine threads.

Nut Sizes

  • Nuts are also commonly referenced using ‘M’ sizes in millimeters (e.g., M3, M8, M12). The size of a metric nut is specified by diameter and pitch dimensions.
  • Hex nuts with diameters under 1/4″ are called hex machine screw nuts.
  • Standard spanner and allen key sizes for commonly used metric nuts include M5, M6, and M8.

Understanding these size specifications is crucial for selecting the right bolts and nuts for various applications based on diameter, thread pitch, length, and other factors.

Thread Types for Bolts and Nuts 

Nuts and bolts are threaded either coarsely or finely.

  • Coarse-threaded nuts and bolts have more space between the threads, so match the threading of a nut to the threading of a bolt. They will be distinguished by a higher thread pitch. Coarse-threaded bolts and nuts may be fastened faster because they are less likely to get stuck or cross-threaded.  
  • Fine-threaded nuts and bolts with smaller thread pitches have less thread gaps, resulting in a tight, strong grip. A fine-threaded bolt’s nut is less likely to be dislodged by vibrations but installing or removing the nut will take longer.

Types of Bolts and Nuts

Types of Bolts

In the industrial sector, various types of bolts are used to meet specific application requirements. Here are some common types of bolts found in industrial settings:

Bolts with Hex Heads

A hex bolt’s hexagonal head serves as a surface for grasping or twisting the bolt with a wrench, socket and ratchet, or drill/driver. Some hex bolts have threads that extend the whole length of the shank and are often used in threaded holes. They provide high grip strength because they distribute tension over the whole bolt. The thicker, unthreaded segment of a partially threaded bolt provides strength to the fastening process. Partially threaded hex bolts are also beneficial for operations that need more force to hold the workpieces together. Hex-head bolts are commonly used in construction and automotive applications.

Carriage Bolts

The domed head of a carriage bolt provides it with a smooth, polished appearance. It also adds a layer of safety and security since it does not have a driving surface like a hex-head bolt. Carriage bolts are fastened with washers and hex nuts after being inserted into pre-drilled holes. The nut is secured to the workpiece by a square area under the head, allowing you to attach it with a single wrench, socket, or driver bit. Carriage bolts are used in a wide range of applications, such as decks, furniture, and outdoor playsets.

Anchor Bolts

Anchor bolts are classified as either those meant for use in concrete foundations or those intended for use in a wall. L-bolts are intended for usage in wet concrete. While the concrete cures, the bolt is kept in place. L-bolts may be used to secure a deck post to a concrete pad. To secure retrofit anchor bolts in existing concrete, an adhesive is employed. When drilling into a wall stud is not possible, toggle bolts provide support for hanging things.


U-bolts have two threaded shanks with a rounded or flattened appearance. Rounded U-bolts are used to secure pipe or conduit to a surface, while squared U-bolts are used to fasten things to a surface, such as a square post. The U-bolt is held in position against the item being secured by two nuts and a metal plate.

Eye bolts

Eye bolts have a loop or ring end and a threaded end for attaching a chain or rope to a wood, metal, or concrete surface. Eye bolts are designed to be used in pre-drilled holes and come with a matching nut. Screw eyes are similar in appearance but have coarser self-tapping threads and a pointed tip that enables them to be driven into a pilot hole in a woodwork item.

Stud Bolts

Stud bolts are threaded rods with threads on both ends, used to secure flanges together in piping systems or other applications where a nut is required on both ends of the bolt. They are commonly used in oil and gas, petrochemical, and power generation industries.

Lag Bolts

Lag bolts, also known as lag screws, have a coarse thread and a hexagonal head designed for use with a wrench or socket. They are used for securing heavy materials to wood, such as attaching lumber to concrete or wood-to-wood connections.

Tension Control Bolts

Tension control bolts feature a unique design with a spline section beneath the head and a cone-shaped washer. They are installed using a specialized wrench that breaks off the spline after reaching the proper tension, providing a reliable and controlled bolt preload. They are commonly used in structural steel connections.

Flange Bolts

Flange bolts have a washer-like flange under the head that distributes the load and provides a larger bearing surface. They are commonly used in automotive, plumbing, and machines.

Types of Nuts

In the industrial sector, there are various types of nuts used for fastening components together. Here are some common types of nuts:

Hexagon Nuts

Hex nuts have a six-sided driving surface. They are a common sort of nut used to connect wood and metal components with bolts of the same size and thread type.

Lock Nuts

Nylon lock nuts have a hexagonal head with an integrated nylon ring. When you tighten a lock nut onto a bolt, the threading of the bolt displaces or deforms the ring, causing friction and preventing loosening from slippage or vibration. A castle nut is a kind of locking nut that works by putting a pin or clip into a hole in the bolt. Rotation is restricted when notches etched into the nut come to rest on the pin.

Wing Nuts

Wing nuts are designed to be tightened and loosened without the need of tools; the wings allow you to tighten and loosen them with your thumb and finger. These nuts are used to make adjustments and removals quick and easy. They may be found on drum sets, light stands, and other items that need to be adjusted on a regular basis.

Cap Nuts

Cap nuts, sometimes known as acorn nuts, are domed and feature a hexagonal driving surface. They are often hand installable. They screw onto the exposed threads of a bolt or threaded rod to protect them and provide a decorative look. Cap nuts may be found in projects like outdoor playsets and fences.

Square Nuts

Square nuts have four flat sides and are designed to be used with square bolts or in channels or tracks where rotation prevention is required. They are commonly used in construction, machinery, and automotive applications.

These different types of nuts cater to specific performance advantages and application scenarios in various industries, ensuring secure fastening of components based on specific requirements and usage scenarios.

How to Choose the Right Bolts and Nuts

Choosing the right bolts and nuts for your project involves considering several factors, such as the material, size, thread type, strength, and environmental conditions. Here is a step-by-step guide to help you select the appropriate bolts and nuts:

  1. Identify the Application Requirements: Determine the specific application requirements such as load-bearing capacity, environmental conditions (temperature, moisture, corrosion), and material compatibility (e.g., compatibility with other materials being fastened).
  2. Select the Material: Choose a material suitable for the intended application. Common materials include steel (carbon steel, stainless steel), brass, aluminum, and titanium. Consider factors such as strength, corrosion resistance, and cost.
  3. Determine Bolt Size and Length: Measure the thickness of the materials being fastened and select a bolt length that provides enough thread engagement for a secure connection. Choose the appropriate bolt diameter (e.g., M6, 1/4 inch) based on the load requirements and the size of the holes in the components.
  4. Select the Thread Type: Determine the appropriate thread type for your application. Common thread types include coarse thread, fine thread, metric thread, and specialized thread. Ensure that the bolts and nuts have compatible threads to ensure a proper fit.
  5. Consider Strength Requirements: Choose bolts and nuts with sufficient strength to withstand the expected loads and stresses. Bolts are typically graded based on their strength. Consider factors such as tensile strength, yield strength, and shear strength when selecting bolts and nuts.
  6. Evaluate Environmental Factors: Consider the environmental conditions in which the fasteners will be used (e.g., exposure to moisture, chemicals, and high temperatures). Select materials and coatings that provide adequate corrosion resistance for the specific environment.
  7. Consider Specialty Features: Depending on the application, you may need specialty features such as locking mechanisms, tamper resistance, or high-temperature resistance. Choose bolts and nuts with the necessary features to meet the specific requirements of your project.

By following these steps and considering the relevant factors, you can choose the right bolts and nuts for your project, ensuring a secure and reliable connection.