Fasteners are hardware devices that are designed to secure two or more parts together for an assembly. The connection may be permanent or non-permanent, and a plethora of fasteners exist to secure parts of all types across many industries. The bolt in particular is a fastener that is commonly used across many applications, and it provides secure attachments for holding materials together, or to position them.
Bolts are considered a type of threaded fastener, meaning that they feature an outer helical ridge, as is also seen on screws. With this threading, the bolt can be passed through a pre-formed hole of components and mate with a correlating nut, allowing for a secure assembly to be produced. Bolts are often thought of as synonymous with screws, but there are some distinctions that set the two fastener types apart. For one, bolts always must be paired with a nut to affix items through the use of axial clamping forces. Screws, on the other hand, are able to create their own hole, boring and digging into the material that they are installed into as torque is applied.
Depending on the application, bolts may come in a variety of materials, shapes, sizes, etc. In general, bolts are constructed from metals such as steel, stainless steel, bronze, titanium, and nylon. Each of these materials provide different uses, such as nylon being beneficial for water applications and steel for its strength. There are also many types of bolts, some examples being anchor bolts, arbor bolts, carriage bolts, elevator bolts, hanger bolts, hex bolts, lag bolts, rock bolts, sex bolts, and shoulder bolts. Bolts will also often greatly differ in the design of their head, each engineered for specific tools to enable an ease of installation or to allow for specific amounts of torque to be applied during installation.
When it is used as an aircraft fastener, bolts are most often constructed from cadmium, corrosion resistant steel, or anodized aluminum alloys. Such fasteners also come in various grades to denote their capabilities and strengths, and these include general purpose, MS, NAS, and AN bolts. For the assembly of an aircraft structure or equipment piece, bolts are most often implemented in areas where there is a need for high strength. These include areas such as the trailing edges, vertical fin, fuselage, wing box, and other flight critical components. Because of their implementation, it is always important that bolts operate with peak efficiency and reliability.