Screw
Introduction
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 a thread. Screws are used to fasten materials by digging in and wedging into a material when turned, while the thread cuts grooves in the fastened material that may help pull fastened materials together and prevent pull-out.
History
The screw is one of the six classical simple machines. The invention of the screw is credited to the ancient Greek scientist Archimedes around 200 BC. The original purpose of the Archimedes' screw was to pump water uphill. The principle of the screw evolved into the idea of using it as a fastener.
Design and Operation
A screw is a combination of simple machines—it is, in essence, an inclined plane wrapped around a central shaft, but the inclined plane (thread) also comes to a sharp edge around the outside, which acts a wedge as it pushes into the fastened material, and the shaft and helix also form a wedge in the form of the point. Some screw threads are designed to mate with a complementary thread, known as a female thread (internal thread), often in the form of a nut, or object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted.
Types of Screws
There are many types of screws, each with unique designs and uses. Some of the most common types include the wood screw, sheet metal screw, deck screw, drywall screw, and machine screw. Each type of screw has a different shape and type of head, which allows for more or less torque to be applied by the screwdriver.
Screw Heads
Screw heads come in various shapes, which can be divided into two main categories: slotted and cross-head. Slotted screws are the simplest, consisting of a single slot into which a flat-blade screwdriver can be inserted. Cross-head screws have a cross-shaped slot, into which a Phillips or Pozidriv screwdriver can be inserted.
Screw Threads
The thread of a screw is the ridge wrapped around the shaft of the screw, often in a helical pattern. The thread is the part of the screw that allows it to dig into the material being fastened and hold securely. The design of the thread also determines how much force is required to drive the screw and how much holding power the screw has.
Screw Materials
Screws can be made from a variety of materials, including steel, stainless steel, brass, bronze, and plastic. The choice of material depends on the application and the environment in which the screw will be used.
Screw Manufacturing
Screw manufacturing involves a series of processes including heading, thread rolling, coating, and packaging. The process begins with a wire rod that is shrunk down to the correct diameter using a series of machines. The rod is then cut into small pieces, which are then headed into a screw shape.
Applications
Screws are used in many applications where it is necessary to fasten two materials together. This includes construction, manufacturing, and home repair. Screws are also used in devices such as screw tops for bottles and jars, and in some types of clamps.