Similar to a screw, the bolt is a fastener made up of a head and an external male thread. They are used in conjunction with a nut to join two unthreaded components. This key difference is what distinguishes a bolt from a screw, the latter being used to join components where at least one has its own thread. Another way to distinguish between a screw and a bolt is the method of assembly. Screws are turned into place where as bolts are usually held in place whilst the nut is tightened. In practice, these definitions are less clear cut as many bolts can be used as screws and vice versa.
The family of bolts is a large one, with dozens of different varieties being produced across the world. They are typically forged components, manufactured by companies such as Brooks Forgings, a manufacturing specialist based in the West Midlands. Here we’ll take a look at some of the most common bolts manufactured right here in the UK and their application in industry.
There are a variety of anchor bolt designs, each designed for attaching objects to structures and concrete. A typical design consists of a hexagonal head upon a standard bolt body. These bolts are used across the construction industry, from family homes to skyscrapers.
The carriage bolt (also known as a coach bolt) has a round or dome shaped head and a square neck, immediately beneath it. This design means the bolt will not rotate when placed into a square hole and hence only one tool is required to install it. Carriage bolts are also commonly used in wood as the square neck provides enough friction to prevent rotation.
Found in applications where head clearance is important, elevator bolts have a square neck and large, circular heads with a flat surface area. They are commonly found in flooring applications but are used in all manner of applications including snow and skateboards. Like the carriage bolt, the elevator bolt is designed not to turn inside the material and so is also useful in timber and wood work-pieces.
An eye bolt is a rather unusually looking bolt as it is designed with a loop at one end. This design allows ropes or cables to be tied to the bolt; ideal in marine and rigging applications. Forged eye bolts are significantly stronger than wire eye bolts, which are bent into place. Eye bolts are also used in lifting applications although care must be taken not to bend the threads by applying lateral forces and loads.
A particularly common bolt is the lag bolt, a bolt designed for specifically for attaching pieces of wood or timber. They are used across the carpentry industry and come is a range of diameters and lengths.
The plough bolt is very similar to the carriage bolt, the only difference being that a plough bolt fits flush into the material. Whilst the head of a standard carriage bolt would protrude from the surface of the work-piece, a plough bolt’s head is sunk into the material. They were originally developed, as the name suggests, for holding together components of a plough.
Step bolts are heavy duty bolts frequently used on transmission towers (such as pylons) and utility poles. They look very similar to carriage bolts although are specifically designed to be used as steps by operators climbing up the tower or pole. As is the case with carriage bolts, the square neck prevents the bolt from turning by providing a grip on the timber of the tower.
A stud bolt is a designed to be used with two nuts, with a thread on either end of its body. They are multi-purpose fasteners designed for permanent or semi-permanent applications. Some common uses include the fastening together two sections of flanged pipe, bolting manhole covers and in car engines.
A U bolt, as the name implies, is a bolt manufactured in the shape of a U. These specialist bolts were initially developed to fasten pipe infrastructure to wood or although their use has now spread to many different applications both domestic and commercial.