The Different Types of Nuts and Bolts Explained (With Pictures!)

Nuts and bolts are two types of fasteners used to join two parts together.

A nut is a small metal object with a hole in the center surrounded by spirally cut grooves known as threads. Nuts are usually hexagonal in shape, which makes them easy to grip from all sides.

They are used as fasteners for mating bolts and are held together by the frictional combination of their threads. Nuts come in a variety of styles, including hex, cap, coupler, wing, turnbuckle, and lock.

A bolt is a long piece of metal with a rounded shank for a body that is threaded in a helical (circular) fashion. The bolt body has a head at one end that allows it to be twisted into an object or nut.

Bolts come in different length sizes while nuts are standard sizes. Bolts are subjected to tensile forces, and it is the tensile stress that causes them to fail.

The key difference between a nut and a bolt is that a nut is a small metal object with a hole in the center surrounded by threads while a bolt is a long piece of metal with a rounded shank that threads the body in a spiral shape. Nuts are used as fasteners for mating bolts, while bolts are used to hold things together.

Let’s learn one by one in detail.

What Are Nuts?

Nuts are mechanical fasteners that are used in conjunction with bolts to secure two or more parts together. They are typically made of metal and have a female thread on the inside, which allows them to be tightened onto a bolt with a corresponding male thread.

Nuts come in a variety of shapes and sizes to fit different types of bolts. For example, hex nuts have a hexagonal shape and are tightened using a wrench, while wing nuts have wing-like protrusions that can be tightened by hand.

There are several types of nuts that are designed to be more secure than others. Lock nuts, for example, have a mechanism that helps to prevent them from coming loose, such as a nylon insert or a series of ridges on the threads. These nuts are often used in applications where it is important to prevent parts from coming loose, such as in the construction of bridges or other structures.

Nuts are commonly made of steel, but they can also be made of other materials such as brass, aluminum, or even plastic. The material used depends on the specific application and the requirements of the fastener, such as its strength, corrosion resistance, and the type of bolt it will be used with.

Nuts are available in a variety of shapes, sizes, materials, and thread patterns. While your selection of a nut is somewhat constrained by your choice of bolt, particularly in terms of size and threading, you still should select the nut head shape and material that is most suitable for your application.

Types of Nuts

There are different types of nuts: cap nuts, castle nuts, coupling nuts, flange serrated nuts, hex finish nuts, hex jam nuts, heavy hex nuts, hex machine nuts, hex machine nuts small pattern, knurled thumb nuts, nylon hex jam nuts, nylon insert lock nuts, prevailing torque lock nuts (stover), slotted hex nuts, square nuts, structural heavy hex nuts, t-nuts, break away or shear nuts, tri-groove nuts, wing nut, and a most common type of nut found today is a hexagonal nut.

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1. Cap Nuts

The cap nut, also known as the acorn nut, gets its name from its shape. The nut has a domed top to prevent contact with the external thread.

2. Castle Nuts

Used with cotter pins to prevent loosening, a castellated nut, also called a castle or slotted nut, is not with slots cut into the top. Used in low-torque applications such as holding a wheel bearing in place.

3. Coupling Nuts

A coupling nut is a threaded fastener used for joining two male threads, most commonly threaded rod. The outside of the fastener is a hex so it can be driven with a wrench.

4. Flange Serrated Nuts

A flange nut is a nut that has a wide flange at one end which acts as an integrated washer that does not move or spin. The serrated flange distributes the pressure of the nut over the part being secured and creates a locking action to prevent loosening.

5. Hex Finish Nuts

Hex finish nuts are used for fastening to a hex cap screw, socket cap screw, or bolt. The most common nuts, hex finish nuts are hex-shaped with internal threads and driven with a wrench.

6. Hex Jam Nuts

A jam nut is often used when a nut needs to be locked in place without clamping to another object. Hex jam nuts are hex-shaped with internal threads, but they are thinner than hex-finish nuts.

7. Heavy Hex Nuts

Larger, heavier, and thicker than a standard hex nut. Heavy hex nuts are hex-shaped, internally threaded, and driven with a wrench. Often used with hex cap screws and carriage bolts.

8. Hex Machine Nuts

A machine nut is hex-shaped with internal threads. Smaller than a hex jam or hex finish nut, they are used with machine screws under 1/4″ in diameter.

9. Hex Machine Nuts Small Pattern

A machine nut is hex-shaped with internal threads. Smaller than a hex jam or hex finish nut, they are used with machine screws under 1/4″ in diameter.

10. Keps-K Lock Nuts

Also known as a keps nut, a k-nut or a washer nut, a keps-k lock nut has an attached free-spinning lock washer. Keps nuts are designed to make assembly more convenient.            

11. Knurled Thumb Nuts

A knurled head thumb nut or thumb nut has a knurled outside surface rather than a hex, which facilitates tightening by hand. Often used in decorative finishes or applications.

12. Nylon Hex Jam Nuts

A low-profile lock nut is hex-shaped and internally threaded with a nylon insert. The nylon material prevents loosening from vibration and cross threads to stop the nut from backing off of the fastener.

13. Nylon Insert Lock Nuts

A nylon insert lock nut is hex-shaped and internally threaded with a nylon insert. The nylon material prevents loosening from vibration and cross threads to stop the nut from backing off of the fastener.

14. Prevailing Torque Lock Nuts (Stover)

Commonly known as stover nuts, prevailing torque lock nuts have chamfered corners and a conical top. The distortion in the top thread resists loosening from vibration. Also called one-way nuts, they can only be installed one way and are often used in high-temperature applications because they are all metal with no nylon insert.

15. Slotted Hex Nuts

Slotted hex nuts are nuts with portions cut out designed to be used with a cotter ping to create a locking mechanism. These nuts are similar to a castle nut but have a lower profile which sometimes makes them a better option.

16. Square Nuts

A four-sided nut that may be flat or beveled on top. Square nuts provide a greater surface contact area which provides more resistance to loosening. Typically mated with square head bolts.

17. Structural Heavy Hex Nuts

Structural hex nuts are comparable to finish nuts but are made to be thicker and much stronger. They are typically used in steel-to-steel structural connections.

18. T-Nuts

A t-nut or tee nut is used to fasten wood, particle or composite board leaving a flush surface. A long thin body with a flange at one end resembles a T in profile. T-nuts often have 3 or 4 prongs that sink into the surface providing better retention.

19. Break Away or Shear Nuts

Shear nuts are cone nuts with a hexagonal gripping point. They are designed with an intentional flaw to snap the hexagonal head off once the maximum torque is reached. Leaving behind a protective cone nut that cannot be easily removed.

20. Tri-Groove Nuts

Tri-groove security nuts have a tapered diameter making them difficult to grip with grabbing devices such as adjustable wrenches or pliers. These nuts require a special unconventional gripping device to install them making them more secure than a typical nut.        

21. Wing Nuts

Wingnuts are threaded nuts with wings on each side of the body allowing for manual turning and installation. Easy hand assembly and used when the nut needs to be removed often.

What Are Bolts?

Bolts are a type of mechanical fastener used to hold two or more objects together. They are typically made of steel or other strong metals and are cylindrical in shape with a head on one end and a screw thread on the other end.

The head of the bolt is used to apply torque to the bolt, allowing it to be tightened or loosened as needed. The screw thread is used to mate with a corresponding nut or threaded hole, which helps hold items securely in place.

There are many different types of bolts designed for specific applications. For example, hex bolts have a hex head that can be tightened or loosened with a wrench. Carriage bolts have a round head with a square neck underneath, which prevents the bolt from turning when tightened. Designed for use in wood, the lag bolt has a square or hexagonal head and a pointed tip.

Bolts are used in a variety of applications including construction, automotive, and manufacturing. Often used to hold together heavy machinery, buildings, and other structures, they are known for their strength and reliability. Some bolts are also coated with a protective varnish to prevent corrosion and extend their life.

Bolts are one of the most versatile structural fasteners, available in a vast array of configurations to suit different materials and strength requirements. These fasteners differ primarily in thread specification, length, and head shape, with varying combinations of these characteristics resulting in bolts with different functions.

They typically require a drilled hole and a complementary nut, or tapped mating part for installation, and, unlike screws, they are generally not tapered. The terminology distinguishing between the types of bolts is often inconsistent and incorrectly used interchangeably for screws, so it’s best to select your bolts based on your project specifications rather than the exact name indicated on a supplier’s website.

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Types of Bolts

Various types of bolts Carriage Bolts, Hex Bolts, U-Bolts, Lag Bolts, T-Head Bolts, Socket Head Bolts, Shoulder Bolts, Penta-Head Bolts, Round Head Bolts, Flange Bolts, Double End Bolts, Machine Screws, toggle bolt, U-bolt, J-bolt, bolt, etc.

1. Carriage Bolts

Carriage Bolts are a form of a self-locking bolt that affords a level of security by using a flush-mount domed head, which permits access to remove or loosen these bolts from the nut side of the bolt only.

Beneath the domed head of the carriage bolt is a square section that can be inserted into a corresponding square cut that is slotted in the material being joined so as to provide the self-locking feature that allows the bolt to be tightened from the nut side without a need to restrain the head with a wrench.

2. Hex Bolts

Hex bolts, also called hexagon head bolts or hexagonal head bolts, are a very common form of bolt that is available in standard dimensional inch and metric sizes. As the name implies, these bolts feature a hexagonal head or a hex head, that is suitable for tightening with a wrench or socket.

A hex bolt may be fully threaded or may feature an unthreaded shoulder. Hex bolts are often used to fasten wood to wood, metal to wood, or metal to metal. Hex nuts and washers are typically used with hex bolts, the washers being valuable for situations where the material being joined is softer and may deform under the tightening force applied to the hex bolt.

Hex bolts are sometimes referred to as hex cap screws when they use a washer face underneath the head and feature a chamfered end. Hex bolts lack those features.

3. U-Bolts

U-bolts are fasteners that are in the shape of the letter U, which contain two male threads, one on each end of the bolt on to which a mounting plate bracket and attachment nuts are placed. While most U-bolts feature a semi-circular profile, some have a squared-off shape.

These fasteners are typically not fully threaded, as they function to clamp an object in place. They are used in a range of applications from supporting pipe to automotive use on drive shafts and exhaust systems. Some designs include rubber coating to preclude wear from the movement of metal against metal.

Other designs of U-bolt add thick rubber gaskets to reduce the effect of vibration and to control noise. Non-metallic designs are also available for use in applications where there is a risk of the U-bolt making contact with an electrically powered conductor.

4. Lag Bolts

lag screws are some of the toughest fasteners. These extremely sturdy fasteners are usually used to connect heavy lumber or other heavy materials that are bearing an intense load.

These screws differ from normal wood, self-drilling or sheet metal screws. Compared to most ordinary screws, lag screws are massive in size. Most lag screws are at least one inch long and ¼-inch thick.

5. T-Head Bolts

T-head bolts or T-slot bolts feature a head design that enables it to be inserted into a slot or recess, thereby securing the bolt in place to prevent it from turning when the securing nut is tightened.

T-bolts are used in applications such as securing fuel tanks in place where having access to both sides of the fastener may not be possible in all cases. The T-slot variety of T-head bolt can be fed into a channel in a machine called a T-slot track and may be used to secure an object at any position along the length of the channel.

6. Socket Head Bolts

Socket head bolts feature a recessed head that is tightened using an Allen wrench or hex socket tool. The head style of these bolts can vary from a cylindrical profile to a flat-head countersunk style to a domed button head design, depending on the desired use.

The deeper recessed Allen socket head affords the ability to increase the torque applied to these fasteners while minimizing the risk of stripping or damaging the head. Socket head bolts are often referred to as socket head cap screws, depending on the supplier.

7. Shoulder Bolts

Shoulder bolts, also called stripper bolts, feature a threaded bolt section of smaller diameter than the shoulder of the bolt (the section of the bolt between the head and the beginning of the threaded portion).

Shoulder bolts are useful for functioning as a shaft or axle that can contain a rotating part, such as a bearing or a bushing.

8. Penta-Head Bolts

Penta-head bolts are an example of a tamper-resistant bolt, which may be used in applications where it is desired to reduce the likelihood that a person armed with standard tools can loosen or remove the bolt.

With the head of the bolt in the shape of a pentagon, a standard wrench or socket set will be incapable of being used on these bolts.

9. Round Head Bolts

Similar in appearance to carriage bolts, round-head bolts do not have the square taper beneath the domed head of the bolt and are typically used to join wood. The softer nature of wood permits the bolt to compress against the surface of the wood and grip by friction to preclude the bolt from turning when the nut is tightened.

10. Flange Bolts

Flange bolts are ones that contain a washer-like surface or flange beneath the head of these fasteners that provide a means to distribute the clamping load over a larger surface area, thereby reducing potential damage to the surface with which these fasteners will mate.

Flange bolts are often used in applications such as plumbing and automotive. Flange bolts are traditionally fabricated from steel or stainless steel and are available in fine and coarse threads and in a variety of grades. The flange may be smooth or serrated, the latter of which helps the fastener grip the mating surface.

11. Double-End Bolts

Double-end bolts are sometimes called stud bolts and feature a threaded portion on each end of the bolt without a traditional head. One end is designed to be threaded into a suitable hole that has been tapped with a mated thread, while the other end protrudes and is threaded to support a nut.

The appearance is similar to that of a threaded rod but is traditionally not threaded over the entire length of the stud and may be threaded differently on each end. Some stud bolts, such as the one shown in the image above, use a screw thread on one end in lieu of bolt threads on both ends.

12. Machine Screws

A machine screw is a screw or bolt with a flat point. Available in a variety of drive types and heads, they fit a wide variety of applications. Often driven into tapped holes. Used with nuts and washers, also known as “stove bolts” or “stovers”.

What Is Locking Nut?

A lock nut, also called a locking nut, is a type of nut that resists loosening under vibration and torque. It is an internally threaded fastener that has locking capabilities either alone or in conjunction with another component.

Ordinary nuts impart a clamping force to a bolt or screw to prevent axial movement. However, if the application involves vibration, there is a risk that the nuts will loosen, and the application will be damaged. This is where lock nuts come into their own: they withstand vibrations and impacts.

There are two types of locknuts: those that use friction to prevent loosening and those that have some form of positive locking device.

Friction lock nuts require more torque to both tighten and loosen, especially during the initial free rotation before they begin to clamp the part. This means they cannot be spun quickly along a long length of filament, greatly increasing the manual assembly time for the application.

Examples of friction lock nuts include castellated nuts, distorted thread lock nuts, and interference thread nuts.

The positive locking nuts are free to rotate for both tightening and loosening, they only lock when positive action is taken to lock them in their current position, such as Inserting a pin. This can allow for both faster assembly and more secure attachment.

Examples of positive locknuts are slotted nuts and nylon locknuts.

FAQs.