Types of bolts and nuts

Whether you’re working on a precision engineering project or assembling flatpack furniture, the types of bolts and nuts you use are a vital consideration.

They form a fundamental component in the vast majority of engineered structures, and so understanding the different bolt types and corresponding nuts is essential for a successful build.

In this blog you will learn about the different types of bolts and nuts available, what they are used for and the differences between them.

What are bolts and nuts and how are they used?

The obvious place to start is with the definition of bolts and nuts. The bolt is the threaded fastener designed to be inserted through holes and secured with a nut. The nut, then, is the threaded ‘ring’ that screws onto the bolt, tightening it into place.

Unlike screws, which cut or form their own threads as they are driven into a material, bolts require a pre-threaded nut or tapped hole. Nails rely on friction rather than threads and are typically permanent fixings. At this point, it is also worth distinguishing between bolts and setscrews; a bolt is commonly part-threaded, whereas a setscrew is fully threaded.

Together, bolts and nuts form a secure fastening system that holds parts together whilst also allowing for disassembly and maintenance. They are ideal where strength, adjustability and repeat access are required, and are commonly used across a range of industries, from construction and electronics to manufacturing and automotive.

Main types of bolts and nuts

There are many types of bolts and nuts available, each suited to different scenarios.

With a range of head shapes, thread designs and tightening methods to choose from, understanding the differences helps ensure the correct fastener for the job.

Below is an at-a-glance comparison of the main types:

Fastener Type	Key Characteristics	Best Uses	Common Materials	Typical Head Types
Hex Bolt	Six-sided external head; strong, reliable, easy to tighten with standard tools	Structural steelwork, heavy machinery, general engineering, construction	Carbon steel, stainless steel, alloy steel	Hexagonal head
Socket Head Cap Screw (Allen Bolt)	Cylindrical head with internal hex drive; compact; high strength; ideal for recessed installations	Precision engineering, machinery, tooling, confined spaces	Alloy steel, stainless steel, titanium	Cylindrical socket head (internal hex)
Eye Bolt	Threaded shank with looped head for attachment; designed for lifting and anchoring	Lifting operations, rigging, construction, load securing	Carbon steel, stainless steel, forged alloy steel	Circular eye/loop head
Wing Bolt	Two protruding wings for hand tightening; tool-free operation; quick adjustment	Light-duty assemblies, access panels, temporary fixings, frequent adjustments	Stainless steel, steel, brass, plastic	Wing head
Security Bolt	Tamper-resistant drive design requiring specialist tools; deters unauthorised removal	Public infrastructure, security installations, electronics enclosures, anti-vandal applications	Stainless steel, hardened steel	Various security heads (pin hex, one-way, Torx security, etc.)
Coach Bolt (Carriage Bolt)	Smooth domed head with square neck to prevent rotation during tightening; tamper-resistant finish	Timber construction, wood-to-metal connections, fencing, structural timberwork	Galvanised steel, stainless steel, zinc-plated steel	Domed round head with square neck
Shear Bolt	Engineered to break at a predetermined torque or load; acts as a mechanical safety device	Machinery protection, overload protection systems, industrial equipment	Carbon steel, alloy steel, stainless steel	Hex head, tamperproof breakaway head
Custom / Bespoke Bolt	Manufactured to exact specifications; tailored dimensions, threads, materials, and performance	Specialised engineering, aerospace, marine, bespoke industrial applications	Any required material (e.g., stainless steel, titanium, Inconel, brass)	Custom to application requirements

Main types of bolts

Hex bolts

Named after its six-sided hexagonal head shape, the hex bolt can be easily tightened or loosened with standard spanners or socket tools. Hex bolts are used for their reliability and strength and are a popular option within construction (particularly steelwork) and heavy machinery.

Socket Head Cap Screws (Allen Bolts)

More commonly referred to as Allen bolts, named after the Allen Manufacturing Company in the US, socket head cap screws have the hexagon set within the cylindrical head, allowing them to sit within a counterbored hole, for example.

Their compact design makes them ideal for confined spaces, and they are widely used in machinery, tooling and precision engineering applications where accuracy and strength are critical.

Eye bolts

Eye bolts have a looped head used for lifting, securing or anchoring loads. They are commonly used in situations where correct load rating and installation are essential. Typical uses include construction, rigging and load handling, where they provide a reliable connection point for hooks, chains or cables.

Wing bolts

Wing bolts are useful fasteners that can be tightened or loosened without the need for tools. This bolt type has protruding ‘wings’, which allow the user to adjust the tightness by hand. They are often used for applications where quick access is required, usually in light-duty scenarios.

Security bolt

Security bolts have head designs that require specialist tools for installation and removal, helping to prevent tampering. They are commonly used to deter theft, vandalism or unauthorised access, for example, within public infrastructure, protective enclosures and electronic equipment.

Coach bolts (Carriage bolts)

Coach bolts, also known as carriage bolts, have a domed head with a square neck. This bolt type is used in timber and structural applications where a smooth, tamper-resistant finish is required. The square bites into the timber or preformed square recess to prevent the bolt from rotating during tightening.

Shear bolts

Shear bolts are unique in the fact that they are designed to break when subjected to excessive load or torque. By snapping at a predetermined point, they protect machinery and equipment from more serious damage. They are often used in industrial and mechanical systems as a safety measure.

Custom / Bespoke bolts

Depending on the exact requirements of the project, custom or bespoke bolts can be manufactured. When very specific criteria, such as dimensions or materials, need to be met, made-to-order precision bolts can be designed and supplied by experts.

Need a custom bolt? Fastenright offers technical support and tailored manufacturing solutions. Contact us for more details: https://www.fastenright.com/contact-and-enquiry

Main types of nuts

Self-locking nut

Self-locking nuts are designed to stay secure and not loosen under vibration or movement, using a nylon insert or controlled metal deformation to create additional friction. These nuts are commonly used in automotive, machinery and mechanical assemblies where joint integrity is critical.

Nyloc Nuts (Nylon Insert)

Nyloc nuts are a type of self-locking nut with a nylon insert which creates friction against the bolt thread. The insert grips the bolt as it is tightened, helping prevent loosening caused by vibration or movement. They are widely used in automotive, machinery and mechanical assemblies.

Security nut

The counterpart to the security bolt, security nuts are designed to prevent removal without the correct specialist tool, and are found in scenarios where unauthorised access must be restricted, for example within public infrastructure and electronics.

Hex nuts

Used with hex bolts, six-sided hex nuts are the most common nut type and are used for a range of general engineering applications.

Barrel nuts

Barrel nuts are internally threaded fasteners used within pre-drilled holes. They can be used where external access is limited or a flush finish is required, such as within furniture assembly, tight spaces or for structural connections.

Custom / Bespoke nuts

Custom or bespoke nuts are manufactured to meet specific industrial requirements where off-the-shelf fasteners are not suitable.

These can include non-standard sizes, thread forms, materials or performance characteristics.

Need a custom nut? Fastenright offers technical support and tailored manufacturing solutions. Contact us for more details.

Bolt Threads, Grades and Materials

Bolts are generally supplied with metric or imperial threads, which must match the nut.

Carbon steel bolts offer high strength and are widely used in structural and machinery applications, while stainless steel bolts offer corrosion resistance.

For steel bolts, the strength is defined by the steel grade, which indicates how much load the fastener can withstand.

Selecting the correct combination of thread type, grade and material ensures long-term performance and reliability.

How to choose the right bolt and nut?

Choosing the correct bolt and nut depends on the specific demands of the application. Key factors include the load being carried, exposure to the elements, vibration levels and security requirements.

It is essential that the bolt and nut are correctly matched in thread type, size and material to ensure safe and reliable performance. With expert technical support and custom manufacturing capability, Fastenright can help identify the most effective fastening solution for each application.

If you need help selecting the right nuts and bolts for your project, or if you have custom requirements, the experienced team at Fastenright can help.