Bolts Types and Sizes: Metric & Imperial Bolt Dimensions Chart

Bolts are a type of essential fastener that often assembled with nuts. Using a bolt with the right sizes is vital for jobs in various machinery and equipment. In this article, we’ll go through a complete guide of bolts, which involves bolts definition, types, dimensions explain, and the standard bolt sizes chart in metric and imperial.

What are Bolts?

Bolts are a kind of externally threaded fastener used with a nut. It will not rotate in the assembly process, but is tightened by turning the nut. The screw is usually inserted into an existing threaded hole or pass through the material to form its own internal thread, and then it is tightened by applying torque to head.

What are the Different Types of Bolts - Types of Bolts and Their Uses

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Anchor bolt
With a threaded part in one end and non-threaded in another end, which can be made in L shape, Pin type, Wedge type, or other forms, often work with steel plates or stiffeners to connect structural and non-structural elements to the concrete, transfer tension forces and shear forces. Anchor bolts come in different types based on the installation method. The simplest and strongest form of anchor bolt is cast-in-place, another type is post-installed anchors.

Carriage bolt
Carriage bolt also called coach bolt, with a round head and square neck, which makes the bolt distinguished from other bolts, also makes it self-locking when it is placed through a square hole and prevent the bolt from turning when tightened. The shank has no threads. It can be installed with only one tool, a spanner or wrench, working from one side. Carriage bolts are usually used to fasten metal to metal or metal to wood. You can find it in security fixings, such as locks and hinges. This kind of bolts was used in a carriage which was the basic transportation during inactive times.

Elevator bolt
Similar to the carriage bolt but elevator bolt with a thin flat or countersunk head and a square undercut, used in conveyor system setups. The head diameter of elevator bolts is larger than other types, which can prevent the bolt from going through soft conveyor material. When you install it, the head of the elevator bolt should lie against the inside surface of the elevator belt with the nuts and washers on the inside of the elevator bucket. Correct installation will make the elevator bolt head fitting snuggly just below the surface of the elevator belt.

Hex bolt

Hex bolts are designed with a hexagonal head that to be driven by a wrench and external machine threads, maybe partially threaded or fully threaded. Steel is one of the most common materials of bolts, but hex bolts may also be made with aluminum, copper, brass, titanium, or even plastic. Hex bolts can be used for infrastructure that requires a strong fastener with high tensile strength properties, they can also be used in tight spaces with limited access because tools can access them from all angles, or fastening wood, steel, or other materials in bridges, buildings, and more construction projects.

Lag bolt
Lag bolts, also known as lag screws, one of the toughest fasteners are extremely sturdy. They are significantly larger than most other screws. This kind of bolt can create its own thread and form friction joint in wood with their coarse threads and other soft materials when tightened, they don’t need nuts, usually used to connect heavy lumber or other heavy materials that are bearing an intense load.

Eyebolt

Eyebolt consists of a threaded shank with a ring or loop at one end, often used to attach an eye to a structure, through which ropes, cables, or shackles can be secured. Eyebolts are commonly found in hardware in material handling, another common use of the bolt is to create a lifting eye to that crane can be attached to machinery. Based on their threading, eyebolts can be divided into machine screw threading and wood screw threading. According to their construction, eyebolts can be classified as the forged and bent eye.

J-bolt
J-bolts are J-shaped fasteners with threads at the non-curved section, another section is designed to a hook for support. J-bolts come in different lengths and diameters, in construction application, it is hook onto the rebar embedded in the concrete. J-bolts are usually used in structural applications, for example, when you erecting a new building or garage, you need to secure walls to concrete foundations with J bolts. They are readily available in many hardware stores.

U-bolt
A U-bolt is in the shape of the letter “U” with threads on both ends, its typical use is to support/clamp pipes through which fluids and gasses pass, and hold ropes together. Now the wider applications of U bolts including clamp any kind of tubing/round bar. A U-bolt would be described by the size of the pipe it is clamping. To determine the correct size u-bolt for your application is important. U-bolts can be made from various materials, durable and non-corrosive metal is the first choice, such as 316 stainless steel, 304 stainless steel, and plain carbon steel.

Shoulder bolt
Shoulder bolts, also known as shoulder screws or stripper bolts, are a type of machine screws that consist of three sections, the long cylindrical non-threaded shoulder is between the head and threads, which allows the attached part to rotate around or slide along its length. The head has the largest diameter, the shoulder is described by its diameter and length, and the diameter of the threaded part is slightly smaller than that of the shoulder. Shoulder bolts usually used to attach pulleys, moving engine parts, gears, rolling wheels, and stripper plates.

Sex bolt
The sex bolt, also known as a barrel bolt, connector bolt, or binding barrel, is a type of mating fastener combining a nut and a screw, it consists of a barrel with internal threads and a screw with external threads, both the barrel and screw have heads designed to clamp material between the head of the barrel and the head of the screw. Some sex bolts have knurled barrels to allow one-sided assembly. Mating fasteners are known by many other different names.

Hanger bolt
Hanger bolts are headless bolts with threads on both ends, used to suspend objects from or attach items to wood, it will add an external thread or create a hidden fastening joint. Hanger bolts feature one side with a self-tapping lag screw thread to grip into the wood, with the other end having machine screw threads to accept a nut or thread into an internally tapped hole.

Flange bolt
The flange bolt has a circular flange under the head that acts like a washer to distribute the load. The ridge surrounding their heads also makes them easy to be identified. Flange bolts feature a nozzle, thereby speeding the assembly while eliminating the washer. They can ensure a reliable, long-lasting connection between two sections of a large and enclosed area. The popular use of flange bolts including car exhaust, Plumbing, electronic devices, and hard-to-reach applications.

There are also machine bolts with a fully threaded shaft and a semi-cone point, used to fasten wood to wood, wood to metal, and metal to metal. Its point will not be chamfered or rounded. Machine bolts can be divided into hex bolts and square bolts based on the head type.

Bolt Dimensions Explained - Metric Bolt Sizes/Dimensions

Metric bolts are referenced using “M” sizes, such as the M8 bolt size. The size of a metric bolt is specified using pitch, diameter, and length in millimeters. For example, in M8-1.0*20, the “M” means the Metric thread designation, the digit 8 refers to the Nominal diameter (in millimeters), 1.0 refers to the pitch, and 20 refers to the length. Sometimes, the pitch is omitted in the abbreviated format, such as M8-20, this means the bolt has a coarse thread. The bolt dimension can also be expressed in imperial units.

1. Diameter: the width of the bolt shank, the bolt head is not included. The defined diameter of metric bolts is actually slightly larger than the actual diameter. So an M8 bolt would have a diameter that’s slightly under 8mm.

2. Pitch: the measurement between the apex of adjacent threads on the bolt’s shank, equal to the ratio of threads to unit length. Metric bolts are available with either coarse or fine thread pitches. Metric bolts with a coarse thread pitch have more threads per inch than comparable imperial bolts.

3. Length: for socket head, pan head, button head, and hex head bolts, the length measurement from the chamfered edge to the undercut of the head, and the bolt head is not included. But for flat head bolts, the length includes the height of the bolt head and for dome head bolts the length is measured from the highest point on the curved head. The length of a metric bolt is measured and defined in exactly the same way as imperial bolts (fasteners).