A screw is a type of fastener, typically made of metal, characterized by a helical ridge, known as a male thread (external thread) or just thread, wrapped around a cylinder. One of the most common uses of screws is to hold objects together and to position objects. They are ubiquitous in mechanical assemblies and woodworking; for instance, screws are often used in furniture, electronics, vehicles, and buildings. The concept of the screw dates back to around 400 BC with the invention of the screw pump by Archytas of Tarentum, which was later developed by Archimedes into the water screw, used for raising water.
The design of a screw allows it to convert rotational force (torque) into linear force and motion. This mechanical advantage is achieved through the screw's thread, which provides a path for the screw to advance in a controlled manner. As the screw is turned, the threads pull it forward or backward depending on the direction of rotation, engaging the material and pulling it tight. This makes the screw an essential tool in many forms of assembly and repair, providing a secure and durable hold when joined with materials like wood, plastic, or metal.
Screws come in various shapes and sizes, each designed for specific applications. The head of a screw is also an important feature, with designs such as flat, Phillips, Torx, and hexagonal, each providing different levels of grip and fitting different types of screwdrivers or bits. The material of the screw is chosen based on the application; common materials include carbon steel, stainless steel, brass, and even titanium for specialized uses. The strength, resistance to corrosion, and ease of driving are all considerations that affect the choice of screw material and design.
Advancements in screw technology continue to evolve with the development of more durable and efficient threading types and drives. Innovations such as the Robertson or square drive (square_drive) and the Pozidriv (Pozidriv) offer more surface contact between the screw and the driver, reducing slip and wear. Furthermore, specialized screws such as the drywall screw or the concrete screw (concrete_screw) cater to specific tasks, enhancing the functionality and efficiency of construction and assembly operations. Understanding the right type of screw for each application is essential for achieving the best results, making the humble screw a fundamental element in modern mechanical design and construction.