Instruct: Given a question, retrieve documents that answer the question.
Query: What are screws most commonly made of?
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.
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.
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.
Most of the following screw drives are considered tamper-resistant because of their obscurity. Tamper-resistant drives are commonly used on equipment such as home electronics, to prevent easy access thereby reducing the incidence of damage or improper repair. Equally, this can prevent people with the relevant technical knowledge from possibly performing a repair without having to return the unit to the manufacturer. However, widespread recent availability of assorted drive bits (including security types) minimizes this advantage, at least for some fastener types. True tamper-resistant screw drives include the breakaway head and one-way screw drives.
An external Torx screw has a projecting head in the shape of a Torx screwdriver bit (instead of a standard recessed cavity); a Torx socket is used to drive it. The external "E" Torx nominal sizing does not correspond to the "T" size (for example, an E40 socket is too large to fit a T40, while an E8 Torx socket will fit a T40 Torx bit). These screws are most commonly encountered in the motor industry.
On a wood router (a hand-held or table-mounted power tool used in woodworking), the collet is what holds the bit in place. In the U.S. it is generally for bits, while in Europe bits are most commonly . The collet nut is hexagonal on the outside so it can be tightened or loosened with a standard wrench, and has threads on the inside so it can be screwed onto the motor arbor.
Plant oils or vegetable oils are oils derived from plant sources, as opposed to animal fats or petroleum. There are three primary types of plant oil, differing both the means of extracting the relevant parts of the plant, and in the nature of the resulting oil:Vegetable fats and oils are what are most commonly called vegetable oils. These are triglyceride-based, and include cooking oils like canola oil, solid oils like cocoa butter, oils used in paint like linseed oil and oils used for industrial purposes. Pressed vegetable oils are extracted from the plant containing the oil (usually the seed), using one of two types of oil press. The most common is the "screw press", which consists of a large-diameter metal screw inside a metal housing. Oil seeds are fed into the housing, where the screws mash the seeds, and create pressure which forces the oil out through small holes in the side of the press. The remaining solids, called "seed cake", are either discarded or used for other purposes. Oil presses can be either manual or powered. The second type of oil press is the "ram press", where a piston is driven into a cylinder, crushing the seeds and forcing out the oil. Ram presses are generally more efficient than screw presses.
The ISO metric screw threads are the worldwide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.
A screw extractor is a tool for removing broken or seized screws. There are two types: one has a spiral flute structure, commonly called an easy out after the trademarked name "EZ-Out"; the other has a straight flute structure. Screw extractors are intentionally made of hard, brittle steel, and, if too much torque is applied, can break off inside the screw that is being removed. Since the extractor is an extremely hard material, and a typical home shop drill bit will not be able to drill into it, a larger element of difficulty is added to the original screw extraction project. One way to avoid this added difficulty is to drill a hole completely through the screw. Thus, if the fastener breaks, a punch can be used to drive out the easy out from the screw, via the back, or end, of the fastener.
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 ​1⁄4 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 = 0.112inches 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]
The distinction between a bolt and a screw is commonly misunderstood. There are several practical differences, but most have some degree of overlap between bolts and screws.
The basic principles of the ISO metric screw thread are defined in international standard ISO 68-1 and preferred combinations of diameter and pitch are listed in ISO 261. The smaller subset of diameter and pitch combinations commonly used in screws, nuts and bolts is given in ISO 262. The most commonly used pitch value for each diameter is the coarse pitch. For some diameters, one or two additional fine pitch variants are also specified, for special applications such as threads in thin-walled pipes. ISO metric screw threads are designated by the letter M followed by the major diameter of the thread in millimeters (e.g. M8). If the thread does not use the normal coarse pitch (e.g. 1.25mm in the case of M8), then the pitch in millimeters is also appended with a multiplication sign (e.g. "M8×1" if the screw thread has an outer diameter of 8mm and advances by 1mm per 360° rotation).
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:
The internal-wrenching square socket drive for screws (as well as the corresponding triangular socket drive) was conceived several decades before the Canadian P. L. Robertson invented the Robertson screw and screwdriver in 1908 and received patents in 1909 (Canada) and 1911 (). An earlier patent covering both square-socket- and triangle-socket-drive wood screws, , was issued to one Allan Cummings of New York City on March 30, 1875. However, as with other clever drive types conceived and patented in the 1860s through 1890s, it was not manufactured widely (if at all) during its patent lifespan due to the difficulty and expense of doing so at the time. Robertson's breakthrough in 1908 was to design the socket's taper and proportions in such a combination that the heads could be easily and successfully cold formed, which is what made such screws a valuable commercial proposition. Today, cold forming (by stamping in a die) is still the common method used for most screws sold, although rotary broaching is also common now. Linear broaching to cut corners into a drilled hole (similar to the action of a mortising machine for woodworking) has also been used (less commonly) over the decades.
VE follows a structured thought process that is based exclusively on "function", i.e. what something "does" not what it is. For example a screw driver that is being used to stir a can of paint has a "function" of mixing the contents of a paint can and not the original connotation of securing a screw into a screw-hole. In value engineering "functions" are always described in a two word abridgment consisting of an active verb and measurable noun (what is being done – the verb – and what it is being done to – the noun) and to do so in the most non-prescriptive way possible. In the screw driver and can of paint example, the most basic function would be "blend liquid" which is less prescriptive than "stir paint" which can be seen to limit the action (by stirring) and to limit the application (only considers paint). This is the basis of what value engineering refers to as "function analysis".
Modern handles, more commonly referred to as "shafts," are made of hollow metal. They are usually octagonal, instead of round, in order to provide a better grip. Most are made of aluminum, titanium, scandium, or alloys, but some shafts are still made from other materials, including wood, plastic, or fiberglass. The open end of the hollow shaft must be covered with tape or a plug (commonly referred to as the "butt" or "butt end" of the stick), usually made of rubber. The head of the stick is usually attached to the shaft with a screw to keep it in place.
Soon after SPS had begun producing the [hex] socket head set screw, Hallowell had the idea to make a [hex] socket head cap screw (SHCS). Hallowell said, "Up to this moment none of us had ever seen a socket head cap screw, and what I am about to relate concerns what I believe was the first socket head cap screw ever made in this country [the U.S.]." SPS gave their line of screws the Unbrako brand name, chosen for its echoing of the word "unbreakable".
The strongest and most reliable type of ice screws currently available are the modern tubular ice screws which range in lengths from 10 to 23 cm. The approximate strength rating on a modern tubular ice screw is around 7 kN, and it has been found that short ice screws in good ice hold about 7-8 kN, no matter what the fall factor or configuration is. The International Climbing and Mountaineering Federation drop test specifies that when multi-pitch lead climbing and the leader has only placed one screw (typically merely clipping one of the anchor screws) before climbing up a couple of meters and falling (a fall factor of 2), the screw must hold. The dynamic ropes used in climbing can mitigate failure of an ice screw by keeping the impact forces low, especially if using a new rope that has not had any previous falls. It is rare that an ice screw fails in fall factors of 1 or less, if placed in good ice.
Screw terminals are commonly used to connect a chassis ground, such as on a record player or surge protector. Most public address systems in buildings also use them for speakers, and sometimes for other outputs and inputs. Alarm systems and building sensor and control systems have traditionally used large numbers of screw terminations.
2. The wider wing nut that sits underneath the center screw controls the placement of the lamp within the reflector. Loosening this wing nut will free the lamp assembly from the cap housing. The user can then push the entire adjustment screw and lamp holder up, down, left or right to center the hot spot in the beam. It is this adjustment that most commonly needs to be made with lights that haven't been regularly serviced. Sometimes it is helpful to use a screwdriver or wrench or other thin tool to reach between the body of the light and the cap to push up on the lamp holder assembly and hold it in place while you tighten the wing nut back down.
The ball screw is a more advanced type of leadscrew that uses a recirculating-ball nut to minimize friction and prolong the life of the screw threads. The thread profile of such screws is approximately semicircular (commonly a "gothic arch" profile) to properly mate with the bearing balls. The disadvantage to this type of screw is that it is not self-locking. Ball screws are prevalent in powered leadscrew actuators.
Reed and Prince, also called Frearson, is another historic cross-head screw configuration. The cross in the screw head is sharper and less rounded than a Phillips, and the bit has 45° flukes and a sharper, pointed end. Also, the Phillips screw slot is not as deep as the Reed and Prince slot. In theory, different size R&P screws fit any R&P bit size.
Pozidriv and the related Supadriv are widely used in Europe and most of the Far East. While Pozidriv screws have cross heads like Phillips and are sometimes thought effectively the same, the Pozidriv design allows higher torque application than Phillips. It is often claimed that they can apply more torque than any of the other commonly used cross-head screwdriver systems, due to a complex fluting (mating) configuration.
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.
In Japan, the male sizes are often designated as DTC-20, DTC-27, DTC-40 (discontinued) and DTC-45 corresponding to a respective screw head size of 3.2mm, 4.6mm, 6.4mm and 7.7mm; with the size of the screw measured across the widest portion of the mating part of the head. The most common sizes in use for consumer electronics are DCT-20 and DTC-27.
One-way screws are special screws that can be turned only in one direction. They are sometimes called one-way clutch screws, but should not be confused with true "clutch" screws. They can be installed with a standard flat-blade screwdriver, but cannot be easily removed using standard tools. One-way screws are commonly used in commercial restroom fixtures and on vehicle registration plates, to prevent vandals from tampering with them.
The body of a wooden pipe can be made of either a coniferous wood or hardwood, although the lower section of the pipe (comprising the foot, cap, block and mouth) will nearly always be made from hardwood to provide a precise edge for the pipe's mouth. Using screws and glue, the pipes are assembled from wooden pieces of various shapes and sizes. In contrast with the circular cross-section of a metal pipe, the cross-section of a wooden pipe is most commonly square or rectangular.