For the construction of aircraft structures and systems, a plethora of fasteners are implemented, sometimes numbering in the millions for a single unit. Fasteners are devices that are used to affix two or more components together, and they often come in the form of bolts, screws, nuts, cables, wires, clamps, and more. Bolts and screws are very common aircraft fasteners that are used extensively during construction, and they are often confused for one another due to some similar aspects and characteristics. With their importance for aircraft construction, it is very beneficial to understand their differences to better be aware of how they may be correctly used.
Both screws and bolts are considered externally threaded fasteners, meaning that they both feature a helical thread that protrudes from the shaft of their bodies. This allows them to mate with other components and hold them together. Bolts are threaded fasteners that most often feature a threaded shaft, as well as a shaped head for tool installation. The purpose of a bolt is to assemble two or more unthreaded components together with the aid of a nut, and this is done by passing the shaft of the bolt through a hole in the component, and then tightening a nut on the opposing side. With the bolt and nut exerting pressure on each side of the assembly, components are held together through axial clamping forces. Bolts are most often used for aircraft construction where there is a need for high strength, and this may include areas such as structures, assemblies, instruments, and more. Bolts may also come in various types depending on the application need, and common bolt types include hex bolts, anchor bolts, eye bolts, and more.
A screw, on the other hand, is a threaded fastener that utilizes its helical, external threading to wedge and dig into the component it is meant to secure while being tightened. By applying torque to the screw head, the screw is driven in and materials are pulled in tightly by the threading to prevent easy removal of the fastener. There are many commonly used screw types, and some examples include concrete screws, self-tapping screws, wood screws, sheet metal screws, and more. Within aerospace construction, screws are most often used in areas in which there is not the need for the strength of a bolt. This may include securing instruments to panels, installing various assemblies, and fastening other non-structural components.
With their various properties and applications, the greatest difference between bolt and screw aircraft fasteners are their method of tightening and installation. While a screw requires torque to be dug into a component and can create its own threading, a bolt requires an existing hole and mating nut to be fastened and installed. Bolts also differ in their installation method due to the fact that torque is not applied to the bolt for tightening, rather to the nut instead. For their load carrying capacity, larger size bolts may be utilized to achieve a higher load carrying capacity, while screws are typically reserved for lower load carrying capacities.