question: Why haven’t we gone to a specific screw type yet?
comment: Different screws are needed for different applications. Some are designed to be "security" screws, some are designed for higher torque, others are made just to be cheap, and some are made for convience.
passages: These fasteners are "screws" according to the "Machinery's Handbook" criteria, and the obsolescent term "lag bolt" has been replaced by "lag screw" in the "Handbook". However, to many tradesmen, they are "bolts", because they are large, with hex or square heads.
  
  Section::::Differentiation between bolt and screw.:United States government standards.
   The TP (or Y-type) security screw drive is similar to the Phillips screw head, but three points rather than four. These specialized screws are usually used on electronics equipment, including most Nintendo hardware, Sanyo and Kyocera cellular telephones, and Fuji digital cameras.
  
  Apple uses Y-type screws to secure the battery on the 2010 and 2011 MacBook Pro, as well as an extremely small type in the Apple Watch, iPhone 7 and iPhone X.
  
  Section::::Tamper-resistant types.:Tri-point-3.
   Section::::Preloading.
   The concept of set screws is centuries old, predating the metal screw by at least several hundred years. Early materials included wood, bone, horn, antler and ivory.
   However, Torx and other drivers have become widely available to the consumer due to their increasing use in the industry. Some other styles fit a three-pointed star recess, and a five-lobed spline with rounded edges instead of the square edges of the Torx™. This is called a Pentalobe.
   Section::::Point types.
   Section::::Differentiation between bolt and screw.:Historical issue.
  
  Old USS and SAE standards defined cap screws as fasteners with shanks that were threaded to the head and bolts as fasteners with shanks that were partially unthreaded. The relationship of this rule to the idea that a bolt by definition takes a nut is clear (because the unthreaded section of the shank, which is called the "grip", was expected to pass through the substrate without threading into it). This is now an obsolete distinction, although large bolts still often have unthreaded sections of shank.
   Section::::Combination drives.:ACR Phillips II Plus.
  
  ACR Phillips II Plus is a screw-drive design that can be driven by a #2 Phillips driver or a #2 Robertson driver, but when driven by a Phillips II Plus Bit, the combination results in a stick-fit interface. 
  
  Section::::Combination drives.:Phillips/square.
   Some screws have heads designed to accommodate more than one kind of driver, sometimes referred to as combo-head or combi-head. The most common of these is a combination of a slotted and Phillips head, often used in attaching knobs to furniture drawer fronts. Because of its prevalence, there are now drivers made specifically for this kind of screw head. Other combinations are a Phillips and Robertson, a Robertson and a slotted, a Torx and a slotted and a triple-drive screw that can take a slotted, Phillips or a Robertson.
   There are many standards governing the material and mechanical properties of imperial sized externally threaded fasteners. Some of the most common consensus standards for grades produced from carbon steels are ASTM A193, ASTM A307, ASTM A354, ASTM F3125, and SAE J429. Some of the most common consensus standards for grades produced from corrosion resistant steels are ASTM F593 & ASTM A193.
  
  Section::::Mechanical classifications.:Metric.
  
  The international standards for metric externally threaded fasteners are ISO 898-1 for property classes produced from carbon steels and ISO 3506-1 for property classes produced from corrosion resistant steels. 
   BULLET::::- The depth of cut screw of a "Bailey" (or "Stanley-Bailey") type metal plane (tool) for the blade to move in the direction of a regulating right hand finger.
  
  BULLET::::- Some Edison base lamps and fittings (such as those formerly used on the New York City Subway) have a left-hand thread to deter theft, since they cannot be used in other light fixtures.
  
  Section::::Design.:Form.
   BULLET::::- B18.6.2 Slotted Head Cap Screws, Square Head Set Screws, And Slotted Headless Set Screws (Inch Series)
  
  BULLET::::- B18.6.3 Machine Screws, Tapping Screws, and Metallic Drive Screws (Inch Series)
  
  BULLET::::- B18.18 Quality Assurance For Fasteners
  
  BULLET::::- B18.24 Part Identifying Number (PIN) Code System Standard for B18 Fastener Products
  
  Section::::Standards & traceability.:For military hardware.
   In addition to screw drives, various nut drives have been designed to make removal difficult without specialized tools. Proprietary examples include T-Groove, Slot-Lok, Pentagon, Tork-Nut, T-Slope and Spanner designs.
  
  Section::::Tamper-resistant types.:Breakaway head.
   A square screw drive uses four-sided fastener heads which can be turned with an adjustable wrench, open-end wrench, or 8- or 12-point sockets. Common in the 19th and early 20th centuries, when it was easier and cheaper to manufacture than most other drives, it is less common today (although still easy to find) because the external hex is now cost-competitive and allows better access for wrenching despite nearby obstructions.
  
  Section::::External drives.:Hex.
   Section::::External drives.
  
  External drives are characterized by a female tool and a male fastener. An advantage of external drive fasteners is that they lack a recess in the head, which can collect water, dirt, or paint, which can interfere with later insertion of a driver tool. Also, some external drives can be engaged from the side, without requiring large inline clearance for tool access, which allows their use in tight spaces such as engines or complex pipework. Because the heads must stand out from the surface they attach to, they are rarely available in countersunk or flush designs.
  
  Section::::External drives.:Square.
   Section::::Hexalobular sockets.:Torx.
   Many modern electrical appliances, if they contain screws, use screws with heads other than the typical slotted or Phillips styles. Torx is one such pattern that has become widespread. It is a spline tip with a corresponding recess in the screw head. The main cause of this trend is manufacturing efficiency: Torx screwdriver tips do not slip out of the fastener as easily as would a Phillips or slotted driver. (Slotted screws are rarely used in mass-produced devices, since the driver is not inherently centered on the fastener.)
   Specialized patterns of security screws are also used, such as the Line Head (LH) style by OSG System Products, Japan, as used in many Nintendo consoles, though drivers for the more common security heads are, again, readily available. Another type of security head has smooth curved surfaces instead of the slot edges that would permit loosening the screw; it is found in public rest room privacy partitions, and cannot be removed by conventional screwdrivers.
  
  Section::::Variations.
  
  Section::::Variations.:Torque screwdrivers.
   In all of these applications, the screw thread has two main functions:
  
  BULLET::::- It converts rotary motion into linear motion.
  
  BULLET::::- It prevents linear motion without the corresponding rotation.
  
  Section::::Design.
  
  Section::::Design.:Gender.
  
  Every matched pair of threads, "external" and "internal", can be described as "male" and "female". For example, a screw has male threads, while its matching hole (whether in nut or substrate) has female threads. This property is called "gender".
  
  Section::::Design.:Handedness.
   One example familiar to laypersons is for the attachment of wheels and spare tires of passenger vehicles to deter theft; one of the lug nuts on each wheel may require a specialized socket provided with the set of lug nuts. Similar security fasteners are also available for bicycle wheels and seats.
  
  Section::::Tamper-resistant types.:Security hex.
   The extra spacing between linked terms below helps the reader to see the correct parsing at a glance.
  
  Section::::Materials.
  
  Screws and bolts are usually made of steel. 
  
  Where great resistance to weather or corrosion is required, like in very small screws or medical implants, materials such as stainless steel, brass, titanium, bronze, silicon bronze or monel may be used.
  
  Galvanic corrosion of dissimilar metals can be prevented (using aluminum screws for double-glazing tracks for example) by a careful choice of material. 
   Section::::Actual mechanical advantage and efficiency.
   On the other hand, a bolt is the male part of a fastener system designed to be accepted by a pre-equipped socket (or nut) of exactly the same thread design.
  
  Section::::Types of screws and bolts.
   BULLET::::- To make them useless to the public (thus discouraging theft), left-handed light bulbs are used in some railway and subway stations.
  
  BULLET::::- Coffin lids are said to have been traditionally held on with left-handed screws.
  
  Section::::Screw threads.
  
  Different shapes (profiles) of threads are used in screws employed for different purposes. Screw threads are standardized so that parts made by different manufacturers will mate correctly.
  
  Section::::Screw threads.:Thread angle.
   It is obvious on inspection that a buttress thread with perpendicular face, operating in a split nut, generates minimal disengagement force when tightened in the normally loaded direction, and thus it is possible to derive quick release devices to, for example, allow rapid repositioning of the movable jaw of a vise without having to rotate the screw by many turns. A screw profile, such as acme, where the thrust face is not perpendicular to the axis, generates a significant disengagement force on a split nut, therefore a more robust controlling mechanism would be required. Quick release vices are readily available. It is not known whether any of them are currently using buttress screws. An expired patent for a clamp using a buttress thread exists and this article describes a vise whose screw thread is disengaged by reverse rotation, which is likely to use a buttress thread, however no currently manufactured devices of that nature have been found at this time (October 2018).
  
presuppositions: Different types of screws work the same.
corrections: Different types of screws are designed for different applications.
raw_presuppositions: Different types of screws work the same. All screws work the same.
raw_corrections: Different types of screws are designed for different applications. Different screws are designed for different purposes, such as torque and security.