What are screws most commonly made of?
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A screw is a type of fastener, in some ways similar to a bolt (see "Differentiation between bolt and screw" below), typically made of metal, and characterized by a helical ridge, known as a "male thread" (external 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. There are many screws for a variety of materials; those commonly fastened by screws include wood, sheet metal, and plastic.
Screw
34132621#2
The most commonly known screw press of this design is said to have been invented by famous Greek mathematician Archimedes and is known as the screw conveyor. The screw conveyor consists of a shaft, which is surrounded by a spiral steel plate, similar in design and appearance to a corkscrew. This design is used in a multitude of screw presses. There are some machines of this and also of similar design that are not screw presses at all - they do not separate solids from liquids but are instead used to fuse them together. An example of this is a mold-filling machine. Plastic pellets are inserted at one end and heat is applied, melting the pellets and discharging them into a mold. Another example is known as a cooker-extruder and is used in the production of snack foods such as pretzels and more.
Dewatering screw press
37386289#3
The material of choice for producing these screws is stainless steel typically 18-8 (303). At the tip of the screw most commonly a stainless steel ball is either pressed or glued into place to provide a single point contact for the surface being moved. Common usage has shown the glue method of attaching the ball to be troublesome in many applications as some commonly used glues (Super Glue) tend to outgas and degrade over time in this application.
Fine adjustment screw
15885469#21
Sheet assembly of light aircraft is accomplished predominantly with rivets of alloys 2017-T4, 2117-T4, or 2024-T4. Self-tapping sheet metal screws are available in aluminum alloys, but cadmium-plated steel screws are employed more commonly to obtain higher shear strength and driveability. Alloy 2024-T4 with an anodic coating is standard for aluminum screws, bolts, and nuts made to military specifications. Alloy 6262-T9, however, is superior for nuts, because of its virtual immunity to stress-corrosion cracking.
Skin (aeronautics)
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There are three steps in manufacturing a screw: "heading", "thread rolling", and "coating". Screws are normally made from wire, which is supplied in large coils, or round bar stock for larger screws. The wire or rod is then cut to the proper length for the type of screw being made; this workpiece is known as a "blank". It is then cold headed, which is a cold working process. Heading produces the "head" of the screw. The shape of the die in the machine dictates what features are pressed into the screw head; for example a flat head screw uses a flat die. For more complicated shapes two heading processes are required to get all of the features into the screw head. This production method is used because heading has a very high production rate, and produces virtually no waste material. Slotted head screws require an extra step to cut the slot in the head; this is done on a "slotting machine". These machines are essentially stripped down milling machines designed to process as many blanks as possible.
The blanks are then polished again prior to threading. The threads are usually produced via thread rolling; however, some are cut. The workpiece is then tumble finished with wood and leather media to do final cleaning and polishing. For most screws, a coating, such as electroplating with zinc (galvanizing) or applying black oxide, is applied to prevent corrosion.
Screw
24596535#4
The most known brand of wine screw caps is Stelvin, which is commonly used in the wine industry as generic trademark for any brand of screwcap. The caps have a long outside skirt, intended to resemble the traditional wine capsule ("foil"), and use plastic PVDC (Polyvinylidene chloride) as a neutral liner on the inside wadding.
Screw cap (wine)
32410#23
Propellers (as well as screws, fans and rotors) are used to move through a fluid. Propellers have been used as toys since ancient times, however it was Leonardo da Vinci who devised what was one of the earliest propeller driven vehicles, the "aerial-screw". In 1661, Toogood & Hays adopted the screw for use as a ship propeller. Since then, the propeller has been tested on many terrestrial vehicles, including the Schienenzeppelin train and numerous cars. In modern times, propellers are most prevalent on watercraft and aircraft, as well as some amphibious vehicles such as hovercraft and ground effect vehicles. Intuitively, propellers cannot work in space as there is no working fluid, however some sources have suggested that since space is never empty, a propeller could be made to work in space.
Vehicle
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The Unified Thread Standard (UTS) is most commonly used in the United States, but is also extensively used in Canada and occasionally in other countries. The size of a UTS screw is described using the following format: X-Y, where X is the nominal size (the hole or slot size in standard manufacturing practice through which the shank of the screw can easily be pushed) and Y is the threads per inch (TPI). For sizes inch and larger the size is given as a fraction; for sizes less than this an integer is used, ranging from 0 to 16. The integer sizes can be converted to the actual diameter by using the formula 0.060 + (0.013 × number). For example, a #4 screw is 0.060 + (0.013 × 4) = 0.060 + 0.052 = 0.112 inches in diameter. There are also screw sizes smaller than "0" (zero or ought). The sizes are 00, 000, 0000 which are usually referred to as two ought, three ought, and four ought. Most eyeglasses have the bows screwed to the frame with 00-72 (pronounced double ought – seventy two) size screws. To calculate the major diameter of "ought" size screws count the number of 0's and multiply this number by 0.013 and subtract from 0.060. For example, the major diameter of a 000-72 screw thread is .060 – (3 x .013) = 0.060 - 0.039 = .021 inches. For most size screws there are multiple TPI available, with the most common being designated a Unified Coarse Thread (UNC or UN) and Unified Fine Thread (UNF or UF). Note: In countries other than the United States and Canada, the ISO Metric Screw Thread System is primarily used today. Unlike most other countries the United States and Canada still use the Unified (Inch) Thread System. However, both are moving over to the ISO Metric System. It is estimated that approximately 60% of screw threads in use in the United States are still inch based.[67]
Screw
13349441#3
The #6-32 UNC is a UTS screw specifying a major thread diameter of which is defined as ; and (threads per inch) which equates to a thread pitch of . The optional UNC specification indicates the standard coarse thread is used which is defined for #6 screws as 32 tpi rendering 'UNC' redundant, however it may be seen when other specifications such as plating or other treatments are also specified. It is by far the most common screw found inside computer cases. It commonly appears in lengths of () and () or less often (). Non-standard metricized lengths such as are also sometimes encountered. Nearly every brand new computer case comes with a bag of these. They are commonly used for the following purposes, however there are many exceptions:
Computer case screws
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Once screw turning machines were in common use, most commercially available wood screws were produced with this method. These cut wood screws are almost invariably tapered, and even when the tapered shank is not obvious, they can be discerned because the threads do not extend past the diameter of the shank. Such screws are best installed after drilling a pilot hole with a tapered drill bit. The majority of modern wood screws, except for those made of brass, are formed on thread rolling machines. These screws have a constant diameter, threads with a larger diameter than the shank, and are stronger because the rolling process does not cut the grain of the metal.
Screw