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From Wikipedia

Screw thread

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. More screw threads are produced each year than any other machine element.

The mechanical advantage of a screw thread depends on its lead, which is the linear distance the screw travels in one revolution. In most applications, the lead of a screw thread is chosen so that friction is sufficient to prevent linear motion being converted to rotary, that is so the screw does not slip even when linear force is applied so long as no external rotational force is present. This characteristic is essential to the vast majority of its uses. The tightening of a fastener's screw thread is comparable to driving a wedge into a gap until it sticks fast through friction and slight plastic deformation.


Screw threads have several applications:

  • Fastening
  • Moving objects linearly by converting rotary motion to linear motion, as in the leadscrew of a jack.
  • Measuring by correlating linear motion to rotary motion (and simultaneously amplifying it), as in a micrometer.
  • Both moving objects linearly and simultaneously measuring the movement, combining the two aforementioned functions, as in a leadscrew of a lathe.

In all of these applications, the screw thread has two main functions:

  • It converts rotary motion into linear motion.
  • It prevents linear motion without the corresponding rotation.



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.


The helix of a thread can twist in two possible directions, which is known as handedness. Most threads are oriented so that a bolt or nut, seen from above, is tightened (the item turned moves away from the viewer) by turning it in a clockwise direction, and loosened (the item moves towards the viewer) by turning anti-clockwise. This is known as a right-handed (RH) thread, because it follows the right hand grip rule (often called, more ambiguously, "the right-hand rule"). Threads oriented in the opposite direction are known as left-handed (LH).

To determine if a particular thread is right or left-handed, look straight at the thread. If the helix of the thread is moving up to the right, it is a right-handed thread and conversely up to the left, a left-handed thread. This holds whether the thread is oriented up or down.

By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have right-handed threads. Left-handed thread applications include:

  • Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession. Examples include:
  • In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left-handed threads.
  • In a situation where neither threaded pipe end can be rotated to tighten/loosen the joint, e.g. in traditional heating pipes running through multiple rooms in a building. In such a case, the coupling will have one right-handed and one left-handed thread
  • In some instances, for example early ballpoint pens, to provide a "secret" method of disassembly.
  • In mechanisms to give a more intuitive action as:
    • The leadscrew of the cross slide of a lathe to cause the cross slide to move away from the operator when the leadscrew is turned clockwise.
    • The depth of cut screw of a "Stanley" type metal plane (tool) for the blade to move in the direction of a regulating right hand finger.

The term chiralitycomes from the Greek word for "hand" and concerns handedness in many other contexts.


The cross-sectional shape of a thread is often called its form or threadform (also spelled thread form). It may be square, triangular, trapezoidal, or other shapes. The terms form and threadform sometimes refer to all design aspects taken together (cross-sectional shape, pitch, and diameters).

Most triangular threadforms are based on an isosceles triangle. These are usually called V-threads or vee-threads because of the shape of the letter V. For 60° V-threads, the isosceles triangle is, more specifically, equilateral. For

Urban area

An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets. Urban areas are created and further developed by the process of urbanization. Measuring the extent of an urban area helps in analyzing population density and urban sprawl, and in determining urban and rural populations. Unlike an urban area, a metropolitan area includes not only the urban area, but also satellite cities plus intervening rural land that is socio-economically connected to the urban core city, typically by employment ties through commuting, with the urban core city being the primary labor market. In fact, urbanized areas agglomerate and grow as the core population/economic activity center within a larger metropolitan area or envelope. In the US, Metropolitan areas tend to be defined using counties or county sized political units as building blocks. Counties tend to be stable political boundaries; economists prefer to work with economic and social statistics based on metropolitan areas. Urbanized areas are a more relevant statistic for determining per capita land usage and densities. Definitions They vary somewhat amongst different nations. European countries define urbanized areas on the basis of urban-type land use, not allowing any gaps of typically more than 200 m, and use satellite imagery instead of census blocks to determine the boundaries of the urban area. In less developed countries, in addition to land use and density requirements, a requirement that a large majority of the population, typically 75%, is not engaged in agriculture and/or fishing is sometimes used. Australia In Australia, urban areas are referred to as "urban centres" and are defined as population clusters of 1000 or more people, with a density of at least 200/km2. Canada According to Statistics Canada, an urban area in Canada is an area with a population of at least 1,000 people where the density is no fewer than 400 persons per square km2. If two or more urban areas are within of each other by road, they are merged into a single urban area, provided they do not cross census metropolitan area or census agglomeration boundaries. China In China, an urban area is an urban district, city and town with a population density higher than 1,500/km2. As for urban districts with a population density lower than that number, only the population that lives in streets, town sites, and adjacent villages is counted as urban population. France In France, an urban area is a zone (aire urbaine) encompassing an area of built-up growth (called an "urban unit" (unité urbaine) - close in definition to the North American urban area) and its commuter belt (couronne périurbaine). Although the official INSEE translation of aire urbaine is "urban area", most North Americans would find the same as being similar in definition to their metropolitan area. Japan In Japan urbanized areas are defined as contiguous areas of densely inhabited districts (DIDs) using census enumeration districts as units with a density requirement of 4000|PD/sqkm|PD/sqmi. New Zealand Statistics New Zealand defines New Zealand urban areas for statistical purposes as a settlement with a population of a thousand people or more. Norway Statistics Norway defines urban areas ("tettsteder") similarly to the other Nordic countries. Unlike in Denmark and Sweden, the distance between each building has to be of less than 50 m, although exceptions are made due to parks, industrial areas, rivers, and similar. Groups of houses less than 400 m from the main body of an urban area are included in the urban area. Philippines With an estimated population of 16,300,000, Metro Manila is the most populous metropolitan area in the Philippines and the 11th in the world. However, the greater urban area is the 5th largest in the world with a population of 20,654,307 people (2010 estimate). The Philippines has twelve more metropolitan areas as defined by the National Economic and Development Authority (NEDA). Metro Angeles, Metro Bacolod, Metro Baguio, Metro Batangas, Metro Cagayan de Oro, Metro Cebu, Metro Dagupan, Metro Davao, Metro Iloilo-Guimaras, Metro Naga, Metro Olongapo. Poland In Poland, official "urban" population figures simply refer to those localities which have the status of towns (miasta). The "rural" population is that of all areas outside the boundaries of these towns. This distinction may give a misleading impression in some cases, since some localities with only village status may have acquired larger and denser populations than many smaller towns. Russia In Russia, only the population residing in cities/towns and urban-type settlements is considered to be "urban". The city/town/urban-settlement designation means usually that the majority of the population is employed in areas other than agriculture, but the exact definitions vary from one federal subject to another. Sweden Urban areas in Sweden (tätorter) are statistically defined localities, totally independent of the administrative subdivision of the country. There are 1940 such localities in Sweden, with a population ranging from 200 to 1,252,000 inhabitants. United Kingdom The United Kingdom's Office for National Statistics has produced census results from urban areas since 1951, since 1981 based upon the extent of irreversible urban development indicated on Ordnance Survey maps. The definition is an extent of at least 20 ha and at least 1,500 census residents. Separate areas are linked if less than 200 m (220 yd) apart. Included are transportation features. The 20 largest urban areas are Greater London Urban Area, West Midlands Urban Area, Greater Manchester Urban Area, West Yorkshire Urban Area, Greater Glasgow, Tyneside, Liverpool Urban Area, Nottingham Urban Area, Sheffield Urban Area, Bristol Urban Area, Greater Belfast, Brighton/Worthing/Littlehampton, Edinburgh, Portsmouth Urban Area, Leicester Urban Area, Bournemouth Urban Area, Reading/Wokingham Urban Area, Teesside, The Potteries Urban Area and Coventry/Bedworth Urban Area United States In the United States there are two categories of urban area. The term urbanized area denotes an urban area of 50,000 or more people. Urban areas under 50,000 people are called urban clusters. Urbanized areas were first delineated in the United States in the 1950 census, while urban clusters were added in the 2000 census. There are 1,371 urban areas and urban clusters with more than 10,000 people. The U.S. Census Bureau defines an urban area as: "Core census block groups or blocks that have a population density of at least 1,000 people per square mile (386 per square kilometer) and surrounding census blocks that have an overall density of at least 500 people per square mile (193 per square kilometer)." The concept of Urbanized Areas as defined by the U.S. Census Bureau is often used as a more accurate gauge of the size of a city, since in different cities and states the lines between city borders and the urbanized area of that city are often not the same. For example, the city of Greenville, South Carolina has a city population under 60,000 and an urbanized area population of over 300,000, while Greensboro, North Carolina has a city population over 200,000 and an urbanized area population of around 270,000 — meaning that Greenville is actually "larger" for some intents and purposes, but not for others, such as taxation, local elections, etc. The largest urban area in the United States is that of New York City, with its city proper population exceeding 8 million and its metropolitan area population almost 19 million. The next four largest urban areas in the U.S. are those of Los Angeles, Chicago, Miami and Philadelphia. About 79 percent of the population of the United States lives within the boundaries of urbanized area as of April, 2000 . Combined, these areas occupy about 2 percent of the United States. The majority of urbanized area residents are suburbanites; core central city residents make up about 30 percent of the urbanized area population (a

From Yahoo Answers

Question:ATHEMATICS Algebra: Algebra of complex numbers, addition, multiplication, conjugation, polar representation, properties of modulus and principal argument, triangle inequality, cube roots of unity, geometric interpretations. Quadratic equations with real coefficients, relations between roots and coefficients, formation of quadratic equations with given roots, symmetric functions of roots. Arithmetic, geometric and harmonic progressions, arithmetic, geometric and harmonic means, sums of finite arithmetic and geometric progressions, infinite geometric series, sums of squares and cubes of the first n natural numbers. Logarithms and their properties. Permutations and combinations, Binomial theorem for a positive integral index, properties of binomial coefficients. Matrices as a rectangular array of real numbers, equality of matrices, addition, multiplication by a scalar and product of matrices, transpose of a matrix, determinant of a square matrix of order up to three, inverse of a square matrix of order up to three, properties of these matrix operations, diagonal, symmetric and skew-symmetric matrices and their properties, solutions of simultaneous linear equations in two or three variables. Addition and multiplication rules of probability, conditional probability, Bayes Theorem, independence of events, computation of probability of events using permutations and combinations. Trigonometry: Trigonometric functions, their periodicity and graphs, addition and subtraction formulae, formulae involving multiple and sub-multiple angles, general solution of trigonometric equations. Relations between sides and angles of a triangle, sine rule, cosine rule, half-angle formula and the area of a triangle, inverse trigonometric functions (principal value only). Analytical geometry: Two dimensions: Cartesian coordinates, distance between two points, section formulae, shift of origin. Equation of a straight line in various forms, angle between two lines, distance of a point from a line; Lines through the point of intersection of two given lines, equation of the bisector of the angle between two lines, concurrency of lines; Centroid, orthocentre, incentre and circumcentre of a triangle. Equation of a circle in various forms, equations of tangent, normal and chord. Parametric equations of a circle, intersection of a circle with a straight line or a circle, equation of a circle through the points of intersection of two circles and those of a circle and a straight line. Equations of a parabola, ellipse and hyperbola in standard form, their foci, directrices and eccentricity, parametric equations, equations of tangent and normal. Locus Problems. Three dimensions: Direction cosines and direction ratios, equation of a straight line in space, equation of a plane, distance of a point from a plane. Differential calculus: Real valued functions of a real variable, into, onto and one-to-one functions, sum, difference, product and quotient of two functions, composite functions, absolute value, polynomial, rational, trigonometric, exponential and logarithmic functions. Limit and continuity of a function, limit and continuity of the sum, difference, product and quotient of two functions, L Hospital rule of evaluation of limits of functions. Even and odd functions, inverse of a function, continuity of composite functions, intermediate value property of continuous functions. Derivative of a function, derivative of the sum, difference, product and quotient of two functions, chain rule, derivatives of polynomial, rational, trigonometric, inverse trigonometric, exponential and logarithmic functions. Derivatives of implicit functions, derivatives up to order two, geometrical interpretation of the derivative, tangents and normals, increasing and decreasing functions, maximum and minimum values of a function, Rolle s Theorem and Lagrange s Mean Value Theorem. Integral calculus: Integration as the inverse process of differentiation, indefinite integrals of standard functions, definite integrals and their properties, Fundamental Theorem of Integral Calculus. Integration by parts, integration by the methods of substitution and partial fractions, application of definite integrals to the determination of areas involving simple curves. Formation of ordinary differential equations, solution of homogeneous differential equations, separation of variables method, linear first order differential equations. Vectors: Addition of vectors, scalar multiplication, dot and cross products, scalar triple products and their geometrical interpretations PHYSICS General: Units and dimensions, dimensional analysis; least count, significant figures; Methods of measurement and error analysis for physical quantities pertaining to the following experiments: Experiments based on using Vernier calipers and screw gauge (micrometer), Determination of g using simple pendulum, Young s modulus

Answers:WOW that's so impressive, I don't think I would be able to handle it. Maybe if I was as smart as you....

Question:I am adding three to four new recepticles in my basement. This will be a new series comming from the box. I will be using a 20amp breaker and 12 gauge wire. I Know how to wire one recepticle, but not sure if i should pigtail the white and black wires from the first recepticle and then continue to every other recepticle in the same mannner. there will be no swithces etc.. and of course i want it to be in parallel.

Answers:Good choice of wire gauge and breaker for 4 outlets. Run wires as you stated to the first outlet using the bottom screws. Start the run for the next outlet using the top screws and do the same at every box. Do not use the "convenient" stick-in connections, use the screws for better continuity and voltage transfer. Last but not least, make sure the ground is firmly connected to each outlet and to the ground bar of the breaker box. Buy a "lighted" plug-in circuit tester at the hardware store and check the continuity of every outlet after wiring. If you have the polarity off or a ground not connected, it will tell you very quickly. They are only a few bucks and well worth it for troubleshooting circuits.

Question:I'm going into 9th grade in a few weeks and i have just received my STAR testing results. I didn't do bad but I didn't do well either. I am planning to major in Science and English. During my middle school years, I was selected into an advanced math class where i skipped a level of math. For English and Science, I have received both advanced scores. For History and Geometry, I had received only proficient scores. If i were planning in enrolling in an ivy league, am I screwed?

Answers:No, colleges don't see any of these scores. Nor do they see the PSAT/NMSQT (Practice SAT/National Merit Scholar Qualifying Test) that you'll probably take early high school, or any state-administered mandatory tests. All they ask for is the SAT Reasoning test (normal SATs), the SAT Subject tests (optional, but if you're applying to the Ivies or other first tier schools, you should definitely take at least two, in the subjects you're strongest in), and the ACT if you take it (more popular among non-New England schools, so the Ivies generally prefer the SATs.) If you're planning on trying for an Ivy, look at this as a learning experience. Look at the subjects you didn't do well in, and make sure you pay extra attention to improving in those areas. Because while this one test may not have any bearing on your acceptance, if you're only receiving proficient scores in class instead of advanced scores (aka, A's), that will. As a side piece of advice: Take the PSAT twice. It only counts for the Merit Scholar competition your junior year, and most people only take it then, then their SATs senior year, but if you're smart enough to be shooting for Ivy's, you're smart enough to be shooting for National Merit Scholars, as well. So take it sophomore year (if your school lets you, mine restricted which sophomores were allowed to take it) so you'll do better as a junior when it counts. Similarly, take your first SAT as a junior instead of as a senior, as long as you feel prepared. That way, if you're not satisfied with your scores, you have more time to improve instead of rushing to take it twice as a senior.


Answers:Basically, the parameter deciding how appropriate an instrument is before being used in a particular situation is its LEAST COUNT. The usual least count of a vernier calipers is usually 0.1mm, so when we are dealing with situations involving measurements not more minute than 0.1 mm we can safely avail of its use. The least count of a GENERAL vernier caliper can be easily determined in the following manner. A vernier caliper consists of a fixed main scale and a sliding vernier scale which, as the name suggests, slides on the main scale. The value of one division on a main scale is 1mm and on the vernier scale there are ten divisions which are equal to nine divisions of a main scale. So the value of each vernier scale mark is 0.9mm(9X1/10). The formula for calculation of the least count of a vernier scale is : Value of one M.S. division - value of one V.S. division, which comes out to be 0.1 mm, hence my statement earlier. Along with this V.C. is also used to measure the internal and external diameters of cylinders, bottles etc. There are instruments which are even more accurate than V.C. such as screw gauge which has a least count of 0.01mm.

From Youtube

Vernier Calliper & Micrometer Screw Gauge :

Psyvariar 2 - Area 0 :Psyvariar 2 - System Buzz: The action of a shot ("cartridge") passing through your mecha's Buzz Field. The Buzz Field is the highlighted circular area surrounding the player character, this field represents the area of effect of the Buzz System. The player's destructable hitbox is only a few pixels dead centre of the Buzz Field Each time a shot or object passes through the Buzz Field it counts as 1 Buzz. The key to Psyvariar is to learn how to interact with enemy shots and surf them rather than evading - you have to un-learn a lot from playing past games. Buzzing shots increases the Neutrino gauge explained next: Neutrino: Buzzing enemy shots will fill the Neutrino Gauge, each time the gauge completely fills a short shield will activate and the player character will gain 1 level. Each time a shield activates, the Neutrino Gauge will reset to a value of 0. However it is possible to refill the Neutrino Gauge and activate another shield, while your current shield is still active - this is a Shield Chain. The rate the Neutrino Gauge fills is determined by the gauge's colour; Red is least active while Blue is most active. Buzzing shots while the Neutrino Gauge is closer to Blue will rapidly fill the gauge and allow for Shield Chains in quick succession - enabling the player to dive into the heart of enemy attacks in safety. A Red Neutrino Gauge will fill very slowly, during this period the player must carefully adjust the Neutrino Gauge position in order to trigger a shield at ...