A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an 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. The most common uses of screws are to hold objects together and to position objects.
Often screws have a head, which is a specially formed section on one end of the screw that allows it to be turned, or driven. Common tools for driving screws include screwdrivers and wrenches. The head is usually larger than the body of the screw, which keeps the screw from being driven deeper than the length of the screw and to provide a bearing surface. There are exceptions; for instance, carriage bolts have a domed head that is not designed to be driven; set screws have a head smaller than the outer diameter of the screw; and J-bolts do not have a head and are not designed to be driven. The cylindrical portion of the screw from the underside of the head to the tip is known as the shank; it may be fully threaded or partially threaded.[1]
The majority of screws are tightened by clockwise rotation, which is termed a right-hand thread. Screws with left-hand threads are used in exceptional cases. For example, when the screw will be subject to anticlockwise forces (which would work to undo a right-hand thread), a left-hand-threaded screw would be an appropriate choice.
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Threaded fasteners either have a tapered shank or a non-tapered shank. Fasteners with tapered shanks are designed to either be driven into a substrate directly or into a pilot hole in a substrate. Mating threads are formed in the substrate as these fasteners are driven in. Fasteners with a non-tapered shank are designed to mate with a nut or to be driven into a tapped hole.
A stainless or carbon steel screw for fastening wood, metal, or other materials into concrete or masonry. Concrete screws are commonly blue in color, with or without corrosion coating.[3] They may either have a Phillips flat head or a slotted hex washer head. Heads sizes range from 0.1875 to 0.375 in (4.76 to 9.52 mm) and lengths from 1.25 to 5 in (32 to 127 mm).
The concrete screw was patented by Vincent Yotti of Melbourne Beach, Florida in 1975,[4] and was presented as a sheet metal screw or lag bolt used to anchor articles to concrete or related material. The concrete screw would be an inexpensive screw of quick application and of greater holding strength than prior concrete anchoring devices such as conventional sheet metal screws.
In the United States, concrete screws are commonly called Tapcons which refers to the brand name created from the definition of "an anchor that taps its own threads into concrete." Other commercial names for the fastener are masonry screw, confast screw, blue screw, self-tapping screw, and Titen.
Screws and bolts are made from a wide range of materials, with steel being perhaps the most common, in many varieties. Where great resistance to weather or corrosion is required, stainless steel, titanium, brass (steel screws can discolor oak and other woods), bronze, monel or silicon bronze may be used, or a coating such as brass, zinc or chromium applied. Electrolytic action from dissimilar metals can be prevented with aluminium screws for double-glazing tracks, for example. Some types of plastic, such as nylon or Teflon, can be threaded and used for fastening requiring moderate strength and great resistance to corrosion or for the purpose of electrical insulation.
Bolted joints are a common application, where screws are used in tension to secure two items together. Bolted joints are usually designed so that the frictional forces between the items is greater than the shear force present at the joint. To achieve this the screw is torqued to value to tension the bolt and compress the items; in essence creating a spring-like assembly. This applied tension is called a preload.
If the shear forces are greater than the frictional forces induced by the preload then the screw shank must be strong enough to withstand the shear force; in these applications a high-strength screw is used.
The numbers stamped on the head of the bolt are referred to the grade of the bolt used in certain application with the strength of a bolt. High-strength steel bolts usually have a hexagonal head with an ISO strength rating (called property class) stamped on the head. And the absence of marking/number indicates a lower grade bolt with low strength. The property classes most often used are 5.8, 8.8, and 10.9. The number before the point is the tensile ultimate strength in MPa divided by 100. The number after the point is 10 times the ratio of tensile yield strength to tensile ultimate strength. For example, a property class 5.8 bolt has a nominal (minimum) tensile ultimate strength of 500 MPa, and a tensile yield strength of 0.8 times tensile ultimate strength or 0.8(500) = 400 MPa.
Tensile ultimate strength is the stress at which the bolt fails. Tensile yield strength is the stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0.2 % offset strain. When elongating a fastener prior to reaching the yield point, the fastener is said to be operating in the elastic region; whereas elongation beyond the yield point is referred to as operating in the plastic region, since the fastener has suffered permanent plastic deformation.
Mild steel bolts have property class 4.6. High-strength steel bolts have property class 8.8 or above.
The same type of screw or bolt can be made in many different grades of material. For critical high-tensile-strength applications, low-grade bolts may fail, resulting in damage or injury. On SAE-standard bolts, a distinctive pattern of marking is impressed on the heads to allow inspection and validation of the strength of the bolt. However, low-cost counterfeit fasteners may be found with actual strength far less than indicated by the markings. Such inferior fasteners are a danger to life and property when used in aircraft, automobiles, heavy trucks, and similar critical applications.
SAE J429 defines the bolt grades for imperial sized bolts and screws. It defines them by grade, which ranges from 0 to 8, with 8 being the strongest. Higher grades do not exist within the specification.[8][9] SAE grades 5 and 8 are the most common.
Head marking | Grade, material, and condition | Nominal size range (in) | Proof strength (ksi) | Yield strength, min. (ksi) | Tensile strength, min. (ksi) | Core hardness (Rockwell) |
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SAE Grade 0[8][11] | Strength and hardness is not specified | ||||
SAE grade 1 ASTM A307[12] Low carbon steel |
1⁄4–1-1⁄2 | 33 | 60 | B70–100 | ||
ASTM A307 - Grade B[12] Low or medium carbon steel |
1⁄4–4 | 60 minimum 100 maximum |
B69–95 | |||
SAE grade 2 Low or medium carbon steel |
1⁄4–3⁄4 | 55 | 57 | 74 | B80–100[13] | |
Greater than 3⁄4 | 33 | 36 | 60 | B70–100[13] | ||
SAE grade 4[14] Medium carbon steel; cold worked |
1⁄4–1-1⁄2 | 100 | 115 | |||
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SAE grade 3[12] Medium carbon steel; cold worked |
1⁄4–1 | 85 | 100 | B70–100 | |
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SAE grade 5 Medium carbon steel; quench and tempered |
1⁄4–1 (inc.) | 85 | 92 | 120 | C25–34[13] |
1–1-1⁄2 | 74 | 81 | 105 | C19–30[13] | ||
ASTM A449 - Type 1[12] Medium carbon steel; quench and tempered |
1–1-1⁄2 (inc.) | 74 | 105 | C19–30 | ||
1-1⁄2–3 | 55 | 90 | Brinell 183–235 | |||
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SAE grade 5.1[15] Low or medium carbon steel; quench and tempered |
No. 6–1⁄2 | 85 | 120 | C25–40 | |
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SAE grade 5.2[15] Low carbon martensitic steel; quench and tempered |
1⁄4–1 | 85 | 120 | C26–36 | |
ASTM A449 - Type 2[15] Low carbon martensitic steel; quench and tempered |
C25–34 | |||||
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ASTM A325 - Type 1[12] Medium carbon steel; quench and tempered |
1⁄2–1 (inc.) | 85 | 92[14] | 120 | C24–35 |
1–1-1⁄2 | 74 | 82[14] | 105 | C19–31 | ||
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ASTM A325 - Type 3[12] Atmospheric corrosion resistant steel; quench and tempered |
1⁄2–1 | 85 | 92[14] | 120 | C24–35 |
1–1-1⁄2 | 74 | 82[14] | 105 | C19–31 | ||
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ASTM A354 - Grade BC[12] Medium carbon alloy steel; quench and tempered |
1⁄4–2-1⁄2 (inc.) | 105 | 109[14] | 125 | C26–36 |
2-1⁄2–4 | 95 | 99[14] | 115 | C22–33 | ||
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SAE grade 7 Medium carbon alloy steel; quench and tempered |
1⁄4–1-1⁄2 | 105 | 115 | 133 | |
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SAE grade 8 Medium carbon alloy steel; quench and tempered |
1⁄4–1-1⁄2 | 120 | 130 | 150 | C32–38[13] |
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ASTM A354 - Grade BD[12] Medium carbon alloy steel; quench and tempered |
1⁄4–2-1⁄2 (inc.) | 120 | 130[17] | 150 | C33–39 |
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2-1⁄2–4 | 105 | 115[17] | 140 | C31–39 | |
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SAE grade 8.2[13] Medium carbon boron martensitic steel; fully kilned, fine grain, quench and tempered |
1⁄4–1 | 120 | 150 | C33–39 | |
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ASTM A490 - Type 1[12] Medium carbon alloy steel; quench and tempered |
1⁄2–1-1⁄2 | 120 | 130[14] | 150 minimum 170 maximum |
C33–38 |
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ASTM A490 - Type 3[12] Atmospheric corrosion resistant steel; quench and tempered |
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18-8 Stainless Stainless steel with 17–19% chromium and 8–13% nickel |
1⁄4–5⁄8 (inc.) | 40 minimum 80–90 typical |
100–125 typical | |||
5⁄8–1 (inc.) | 40 minimum 45–70 typical |
100 typical | ||||
Over 1 | 80–90 typical |
The international standard for metric screws is defined by ISO 898, specifically ISO 898-1. SAE J1199 and ASTM F568M are two North American metric standards that closely mimic the ISO standard. In case of imperial sizes the grade is dictated by the number of radial shapes plus a value of two. And imperial bolts use integer values to indicate grades but metric bolts use numbers with one decimal. The two North American standards use the same property class markings as defined by ISO 898.[18] The ASTM standard only includes the following property classes from the ISO standard: 4.6, 4.8, 5.8, 8.8, 9.8, 10.9, and 12.9; it also includes two extra property classes: 8.8.3 and 10.9.3.[19] ASTM property classes are to be stamped on the top of screws and it is preferred that the marking is raised.[20]
Head marking | Grade, material, and condition | Nominal size range (mm) | Proof strength (MPa) | Yield strength, min. (MPa) | Tensile strength, min. (MPa) | Core hardness (Rockwell) |
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Class 3.6[21] | 1.6–36 | 180 | 190 | 330 | B52–95 |
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Class 4.6 Low or medium carbon steel |
5–100 | 225 | 240 | 400 | B67–95 |
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Class 4.8 Low or medium carbon steel; fully or partially annealed |
1.6–16 | 310 | 340 | 420 | B71–95 |
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Class 5.8 Low or medium carbon steel; cold worked |
5–24 | 380 | 420 | 520 | B82–95 |
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Class 8.8[10] Medium carbon steel; quench and tempered |
Under 16 (inc.) | 580 | 640 | 800 | |
17–72 | 600 | 660 | 830 | C23–34 | ||
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Class 8.8 low carbon Low carbon boron steel; quench and tempered |
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Class 8.8.3[19] Atmospheric corrosion resistant steel; quench and tempered |
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ASTM A325M - Type 1[22][23] Medium carbon steel; quench and tempered |
12–36 | ||||
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ASTM A325M - Type 3[22][23] Atmospheric corrosion resistant steel; quench and tempered |
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Class 9.8 Medium carbon steel; quench and tempered |
1.6–16 | 650 | 720 | 900 | C27–36 |
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Class 9.8 low carbon Low carbon boron steel; quench and tempered |
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Class 10.9 Alloy steel; quench and tempered |
5–100 | 830 | 940 | 1040 | C33–39 |
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Class 10.9 low carbon Low carbon boron steel; quench and tempered |
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Class 10.9.3[19] Atmospheric corrosion resistant steel; quench and tempered |
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ASTM A490M - Type 1[22][24] Alloy steel; quench and tempered |
12–36 | ||||
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ASTM A490M - Type 3[22][24] Atmospheric corrosion resistant steel; quench and tempered |
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Class 12.9 Alloy steel; quench and tempered |
1.6–100 | 970 | 1100 | 1220 | C38–44 |
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A2[10] Stainless steel with 17–19% chromium and 8–13% nickel |
Up to 20 | 210 minimum 450 typical |
500 minimum 700 typical |
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ISO 3506-1 A2-50[citation needed] 304 stainless steel-class 50 (annealed) |
210 | 500 | ||||
ISO 3506-1 A2-70[citation needed] 304 stainless steel-class 70 (cold worked) |
450 | 700 | ||||
ISO 3506-1 A2-80[citation needed] 304 stainless steel-class 80 |
600 | 800 |
Some varieties of screw are manufactured with a break-away head, which snaps off when adequate torque is applied. This prevents tampering and also provides an easily-inspectable joint to guarantee proper assembly. An example of this is the shear bolts used on vehicle steering columns, to secure the ignition switch.
Part of the series on | |
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Screw drive types | |
Slotted (flat or straight) | |
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Phillips ("crosshead") PH |
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Pozidriv (SupaDriv) PZ |
Square | |
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Robertson (square) |
Hex | |
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Hex socket (Allen) |
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Torx T, TS, TX |
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Tri-Wing |
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Torq-set |
Spanner head (Snake-eye) |
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Triple square XZN |
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Polydrive |
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One-way |
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Spline drive |
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Double hex |
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Bristol |
Modern screws employ a wide variety of drive designs, each requiring a different kind of tool to drive in or extract them. The most common screw drives are the slotted and Phillips; hex, Robertson, and torx are also common in some applications. Some types of drive are intended for automatic assembly in mass-production of such items as automobiles. More exotic screw drive types may be used in situations where tampering is undesirable, such as in electronic appliances that should not be serviced by the home repair person.
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 which can take a slotted, Phillips or a Robertson. The Recex drive system claims it offers the combined non-slip convenience of a Robertson drive during production assembly and Phillips for after market serviceability. Quadrex is another Phillips/Robertson drive. Phillips Screw Company offers both Phillips and Pozidriv combo heads with Robertson.
Combined slotted/pozidriv heads are so ubiquitous in electrical switchgear to have earned the nickname 'electricians screws' (the first screwdriver out of the toolbox is used - the user does not have to waste valuable time searching for the correct driver). Their rise to popular use has been in spite of the fact that neither a flat screwdriver or pozidriv screwdriver are fully successful in driving these screws to the required torque. Some screwdriver manufacturers offer matching screwdrivers and call them 'contactor screwdrivers', although the original concept of not needing to search for a particular driver is defeated as a contractor screwdriver is useless for non-combination heads. Slotted/philips (as opposed to slotted/pozidriv) heads occur in some North American made switchgear.
The general theory of tamper-resistant fasteners is to make a fastener whose loosening requires a tool that a tamperer is unlikely to have on hand at the time of opportunity for tampering. There is no expectation that it will be impossible for a tamperer to obtain the driver. Rather, the main idea is simply that most tamperers will not bother to seek out and obtain a driver. In the case of end-users, this reduces the incidence of do-it-yourself repair or modifications and any resulting injury, product damage or loss of profit from repairs for the manufacturer. In the cases of vandalism prevention and theft prevention, since most vandalism and theft incidents are simply crimes of easy opportunity, the idea is to "raise the bar" and make the opportunity less convenient.
Many screw drives, including Phillips, torx, and hex socket, have tamper-resistant variants. These typically have a pin protruding in the center of the screw head, necessitating a special tool for extraction. In some variants the pin is placed slightly off-center, requiring a correspondingly shaped bit. However, the bits for many tamper-resistant screw heads are now readily available from hardware stores, tool suppliers and through the Internet. There are also many commonly used techniques to extract tamper resistant screws without the correct driver — for example, the use of an alternative driver that can achieve enough grip to turn the screw, modifying the head to accept an alternative driver, forming one's own driver by melting an object into the head to mould a driver, or simply turning the screw using a pair of locking pliers. Thus, these special screws offer only modest security. However, it is often enough to discourage the more opportunistic varieties of vandalism.
The slotted screw also comes in a tamper-resistant one-way design with sloped edges; the screw can be driven in, but the bit slips out in the reverse direction. One-way screws can be removed using a screw extractor like any other safety screw.
There are specialty fastener companies that make unusual, proprietary head designs, featuring matching drivers available only from them, and only supplied to registered owners[27]. These tend to be confined to industrial uses that the average layperson does not have contact with. But one example familiar to laypersons is the attachment for the wheels and/or spare tires of some types of car; one of the nuts may require a specialized socket (provided with the car) to prevent theft. Security fasteners are also available for bicycle wheels and seats to prevent theft.
The breakaway bolt is a high-security fastener that is extremely difficult to remove. It consists of a counter-sunk flat head screw, with a thin shank and hex head protruding from the flat head. The hex head is used to drive the bolt into the countersunk hole, then the wrench or hammer is used to knock the shank and hex head off of the flat head, leaving only a smooth screw head exposed. Removal is facilitated by drilling a small hole part way into the outer part of the head and using a screw extractor or a punch and hammer at a sharp angle in a counter-clockwise direction. This type of screw is used primarily in prison door locks, but also has considerable usage in the fastening of street signs to sign posts by municipal public works departments.
The hand tool used to drive in most screws is called a screwdriver. A power tool that does the same job is a power screwdriver; power drills may also be used with screw-driving attachments. Where the holding power of the screwed joint is critical, torque-measuring and torque-limiting screwdrivers are used to ensure sufficient but not excessive force is developed by the screw. The hand tool for driving hex head threaded fasteners is a spanner (UK usage) or wrench (US usage).
There are many systems for specifying the dimensions of screws, but in much of the world the ISO metric screw thread preferred series has displaced the many older systems. Other relatively common systems include the British Standard Whitworth, BA system (British Association), and the Unified Thread Standard.
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., 1.25 mm 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 8 mm and advances by 1 mm per 360° rotation).
The nominal diameter of a metric screw is the outer diameter of the thread. The tapped hole (or nut) into which the screw fits, has an internal diameter which is the size of the screw minus the pitch of the thread. Thus, an M6 screw, which has a pitch of 1 mm, is made by threading a 6 mm shank, and the nut or threaded hole is made by tapping threads in a hole somewhat smaller than 6 mm.
Metric hexagon bolts, screws and nuts are specified, for example, in British Standard BS 4190 (general purpose screws) and BS 3692 (precision screws). The following table lists the relationship given in these standards between the thread size and the maximal width across the hexagonal flats (wrench size):
ISO metric thread | M1.6 | M2 | M2.5 | M3 | M4 | M5 | M6 | M8 | M10 | M12 | M16 | M20 | M24 | M30 | M36 | M42 | M48 | M56 | M64 |
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Wrench size (mm) | 3.2 | 4 | 5 | 5.5 | 7 | 8 | 10 | 13 | 17 | 19 | 24 | 30 | 36 | 46 | 55 | 65 | 75 | 85 | 95 |
In addition, the following non-preferred intermediate sizes are specified:
ISO metric thread | M7 | M14 | M18 | M22 | M27 | M33 | M39 | M45 | M52 | M60 | M68 |
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Wrench size (mm) | 11 | 22 | 27 | 32 | 41 | 50 | 60 | 70 | 80 | 90 | 100 |
The first person to create a standard (in about 1841) was the English engineer Sir Joseph Whitworth. Whitworth screw sizes are still used, both for repairing old machinery and where a coarser thread than the metric fastener thread is required. Whitworth became British Standard Whitworth, abbreviated to BSW (BS 84:1956) and the British Standard Fine (BSF) thread was introduced in 1908 because the Whitworth thread was too coarse for some applications. The thread angle was 55° and a depth and pitch of thread that varied with the diameter of the thread (i.e., the bigger the bolt, the coarser the thread). The spanner size is determined by the size of the bolt, not the distance between the flats.
The most common use of a Whitworth pitch nowadays is in all UK scaffolding. Additionally, the standard photographic tripod thread, which for small cameras is 1/4" Whitworth (20 tpi) and for medium/large format cameras is 3/8" Whitworth (16 tpi). It is also used for microphone stands and their appropriate clips, again in both sizes, along with "thread adapters" to allow the smaller size to attach to items requiring the larger thread.
A later standard established in the United Kingdom was the British Association (BA) screw threads, named after the British Association for Advancement of Science. Screws were described as "2BA", "4BA" etc., the odd numbers being rarely used, except in equipment made prior to the 1970s for telephone exchanges in the UK. This equipment made extensive use of odd-numbered BA screws, in order—it may be suspected—to reduce theft.
While not related to ISO metric screws, the sizes were actually defined in metric terms, a 0BA thread having a 6 mm diameter and 1 mm pitch. Other threads in the BA series are related to 0BA in a geometric series with the common factor 0.9. For example, a 4BA thread has diameter (6.0 x 0.9^4) mm and pitch (1.0 x 0.9^4) mm. Although 0BA has the same diameter and pitch as ISO M6, the threads have different forms and are not compatible.
BA threads are still common in some niche applications. Certain types of fine machinery, such as moving-coil meters and clocks, tend to have BA threads wherever they are manufactured.
The Unified Thread Standard (UTS) is most commonly used in the United States of America, 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 practise through which the shaft 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. 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).
In antiquity, the screw was first used as part of the screw pump of Sennacherib, King of Assyria, for the water systems at the Hanging Gardens of Babylon and Nineveh in the 7th century BC.[28]
The screw was later described by the Greek mathematician Archytas of Tarentum (428 – 350 BC). By the 1st century BC, wooden screws were commonly used throughout the Mediterranean world in devices such as oil and wine presses. Metal screws used as fasteners did not appear in Europe until the 1400s.[citation needed]
In 1744, the flat-bladed bit for the carpenter's brace was invented, the precursor to the first simple screwdriver. Handheld screwdrivers first appeared after 1800.
Prior to the mid-19th century, cotter pins or pin bolts, and "clinch bolts" (now called rivets), were used in shipbuilding.
The metal screw did not become a common fastener until machine tools for mass production were developed at the end of the 18th century. In the 1770s, English instrument maker Jesse Ramsden (1735-1800) invented the first satisfactory screw-cutting lathe. The British engineer Henry Maudslay (1771-1831) patented a screw-cutting lathe in 1797; a similar device was patented by David Wilkinson in the United States in 1798. These developments caused great increase in the use of threaded fasteners. Standardization of threadforms began almost immediately, but it was not quickly completed; it has been an evolving process ever since.
The development of the turret lathe (1840s) and of the screw machine (1870s) drastically reduced the unit cost of threaded fasteners by increasingly automating the machine tool control. This cost reduction spurred ever greater use of screws.
Throughout the 19th century, the most commonly used forms of screw head (drive) were simple internal-wrenching slots and external-wrenching squares and hexagons. These were easy to machine and served most applications adequately. The 20th century saw the development of many other types of drive. In 1908, Canadian P. L. Robertson invented the internal-wrenching square drive. The internal-wrenching hexagon drive (hex socket) shortly followed in 1911. In the early 1930s, the Phillips-head screw was invented by Henry F. Phillips.
Threadform standardization further improved in the late 1940s, when the ISO metric screw thread and the Unified Thread Standard were defined.
Alternative fastening methods are nails, rivets, roll pins, pinned shafts, welding, soldering, brazing, and gluing (including taping), and clinch fastening.
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of screws]]
A screw is a sharp piece of threaded metal similar to a nail. Unlike a nail, a screw has spiraling grooves down its spike. A screw is pressed down against wood and spun with a screwdriver so the wood goes into the grooves. This prevents the screw from falling out, as a nail could. Screws are basically divided into wood screws, machine screws and self-tapping screws.
Machine screws have threads which have to be matched with nuts with female threads. Screws can be made of iron, steel, brass, bronze, etc.
Screw threads are measured either in millimeters or in numbers. screws are used in furniture, doors, appliances, mechanical applications etc.
Screwing is the neatest way of holding together to materials. If no glue is involved, then the screwing can be dismantled. Screwing can be used to connect all materials.
These are three different types of screw.
Do not place screws in line as this weakens the wood. Use the right size screwdriver for the screw head. A screwdriver that is too slim can damage the slot, too wide can tear the materials.
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