The construction of drawings is not an easy task, but without it in the modern world it is impossible. Indeed, in order to make even the most ordinary item (a tiny bolt or nut, a shelf for books, the design of a new dress and the like), you must first carry out the appropriate calculations and draw a drawing of the future product. However, often it is one person, and another is engaged in the manufacture of something according to this scheme.
In order to avoid confusion in understanding the depicted object and its parameters, symbols of length, width, height and other quantities used in the design have been adopted throughout the world. What are they? Let's find out.
Quantities
Area, length, width, height and other designations of a similar nature are not only physical, but also mathematical values.
Their single letter designation (used by all countries) was established in the middle of the twentieth century by the International System of Units (SI) and is still used today. It is for this reason that all such parameters are denoted by Latin, not Cyrillic letters or Arabic script. In order not to create separate difficulties, when developing standards for design documentation in most modern countries, it was decided to use almost the same conventions that are used in physics or geometry.
Any graduate of the school remembers that depending on whether a two-dimensional or three-dimensional figure (product) is depicted in the drawing, it has a set of basic parameters. If there are two dimensions - this is the width and length, if there are three of them - then the height is also added.
So, for starters, let's find out how to correctly designate the length, width, height in the drawings.
Width
As mentioned above, in mathematics, the considered value is one of the three spatial dimensions of any object, provided that its measurements are made in the transverse direction. So what is famous for width? Designation with the letter "B" it has. This is known all over the world. Moreover, according to GOST, the use of both capital and lowercase Latin letters is permissible. Often the question arises as to why such a letter is chosen. After all, usually the reduction is made by the first letter of the Latin, Greek or English name of the quantity. The width in English will look like "width".
Probably, the point here is that this parameter was most widely used initially in geometry. In this science, describing the figures, often the length, width, height are denoted by the letters "a", "b", "c". According to this tradition, when choosing the letter “B” (or “b”) was borrowed by the SI system (although other two geometric symbols were used for the other two dimensions).
Most believe that this was done so as not to confuse the width (designation with the letter "B" / "b") with the weight. The fact is that the latter is sometimes referred to as “W” (short for the English name weight), although the use of other characters (“G” and “P”) is also permissible. According to the international norms of the SI system, the width is measured in meters or their multiple (fractional) units. It is worth noting that in geometry it is sometimes also acceptable to use “w” to denote widths, but in physics and other exact sciences such a notation is usually not used.
Length
As already mentioned, in mathematics, length, height, width are three spatial dimensions. Moreover, if the width is a linear dimension in the transverse direction, then the length is in the longitudinal. Considering it as a quantity of physics, we can understand that this word means a numerical characteristic of the length of lines.
In English, this term is called length. It is because of this that this value is indicated by the capital or lower case initial letter of the word - “L”. Like width, length is measured in meters or their multiple (fractional) units.
Height
The presence of this quantity indicates that we have to deal with a more complex - three-dimensional space. Unlike length and width, height numerically characterizes the size of an object in the vertical direction.
In English, it is written as "height". Therefore, according to international standards, it is denoted by the Latin letter “H” / “h”. In addition to height, sometimes this letter appears in the drawings as a designation as depth. Height, width and length - all of these parameters are measured in meters and their multiple and fractional units (kilometers, centimeters, millimeters, etc.).
Radius and diameter
In addition to the parameters considered, when drawing up drawings, one has to deal with others.
For example, when working with circles, it becomes necessary to determine their radius. This is the name of the segment that connects the two points. The first of these is the center. The second is located directly on the circle itself. In Latin, this word looks like "radius". Hence the generally accepted abbreviation: lowercase or capital “R” / “r”.
Drawing a circle, in addition to the radius, one often has to deal with a phenomenon close to it - diameter. It is also a segment connecting two points on a circle. Moreover, he necessarily passes through the center.
Numerically, the diameter is equal to two radii. In English, this word is written like this: "diameter". Hence the abbreviation - large or small Latin letter "D" / "d". Often the diameter in the drawings is indicated by a crossed circle - “Ø”.
Although this is a common abbreviation, it is worth bearing in mind that GOST provides for the use of only the Latin "D" / "d".
Thickness
Most of us remember school math lessons. Even then, teachers said that the Latin letter "s" is used to denote such a value as area. However, according to generally accepted standards, a completely different parameter is recorded in the drawings in this way - thickness.
Why is that? It is known that in the case of height, width, length, lettering could be explained by their spelling or tradition. That's just the thickness in English looks like "thickness", and in the Latin version - "crassities". It is also not clear why, unlike other quantities, thickness can only be indicated with a lowercase letter. The designation "s" is also used to describe the thickness of pages, walls, edges and so on.
Perimeter and Area
Unlike all the values listed above, the word "perimeter" came not from Latin or English, but from Greek. It is formed from "περιμετρέο" ("measure the circumference"). And today this term has retained its meaning (the total length of the borders of the figure). Subsequently, the word fell into the English language ("perimeter") and was fixed in the SI system in the form of an abbreviation with the letter "P".
Area is a value showing the quantitative characteristic of a geometric figure that has two dimensions (length and width). Unlike all of the above, it is measured in square meters (as well as in fractional and multiple units). As for the letter designation of the area, it differs in different areas. For example, in mathematics it is a Latin letter “S”, familiar to everyone from childhood. Why so - no information.
Some unknowingly think that this is due to the English spelling of the word "square". However, in it the mathematical area is “area”, and “square” is the area in architectural sense. By the way, it’s worth remembering that “square” is the name of the geometric figure “square”. So you should be careful when studying drawings in English. Due to the translation of "area" in certain disciplines, the letter "A" is used as a designation. In rare cases, “F” is also used, but in physics this letter means a quantity called “force” (“fortis”).
Other common abbreviations
Designations of height, width, length, thickness, radius, diameter are the most used in the preparation of drawings. However, there are other quantities that are also often present in them. For example, the lowercase "t". In physics, this means “temperature”, however, according to GOST of the Unified System for Design Documentation, this letter is a step (coil springs, rivet joints and the like). However, it is not used when it comes to gears and threads.
The capital and lowercase letter “A” / “a” (according to the same standards) in the drawings is used to indicate not the area, but the center-to-center distance. In addition to various values, in the drawings often have to designate angles of different sizes. To do this, it is customary to use lowercase letters of the Greek alphabet. The most used are “α”, “β”, “γ” and “δ”. However, it is permissible to use others.
What standard defines the letter designation of length, width, height, area and other quantities?
As already mentioned above, so that there is no misunderstanding when reading the drawing, representatives of different nations adopted common standards for letter designation. In other words, if you doubt the interpretation of this or that abbreviation, look at the state standard specifications. This way you will learn how to correctly indicate height, width, length, diameter, radius, and so on.
For the Russian Federation, this regulatory document is GOST 2.321-84. It was introduced back in March 1984 (during the Soviet era), instead of the outdated GOST 3452-59.