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Type of Limits and Fits
极限和配合的类型
The ISO System of Limits and Fits, widely used in a number of leading metric countries, is considerably more complex than the ANSI system.
在一些最主要采用公制的国家中广泛使用的ISO的极限和配合系统，比ANSI的极限和配合系统要复杂得多。
In this system, each part has a basic size. Each limit of size of a part, high and low, is defined by its deviation from the basic size, the magnitude and sign being obtained by subtracting the basic size from the limit in question. The difference between the two limits of size of a part is called the tolerance, an absolute amount without sign.
在这个系统中，每个零件都有基本尺寸。零件尺寸的每一极限，不管大小，都通过对基本尺寸的偏差来定义，其量值和符号由正被讨论的极限减去基本尺寸得到。零件尺寸的两个极限之差称为公差，这是一个没有符号的绝对量值。
There are three classes of fits: 1) clearance fits, 2) transition fits (the assembly may have either clearance or interference), and 3) interference fits.
存在三种配合 1)间隙配合2)过渡配合(装配后可以有间隙或过盈)和3)过盈配合。
Either a shaft-basis system or a hole-basis system may be used. For any given basic size, a range of tolerances and deviations may be specified with respect to the line of zero deviation, called the zero line.
基轴制或基孔制均可采用。对任何给定的基本尺寸，公差范围和偏差可以相对于被称为零线的零偏差线来确定。
The tolerance is a function of the basic size and is designated by a number symbol, called the grade—thus the tolerance grade.
公差是基本尺寸的函数 并通过一个被称为等级的数字符号标明—即公差等级。
The position of the tolerance with respect to the zero line also a function of the basic size—is indicated by a letter symbol (or two letters), a capital letter for holes and a lowercase letter for shafts. Thus the specification for a hole and shaft having a basic size of 45 mm might be 45H8/g7.
公差相对于零线的位置同样为基本尺寸的函数通过一个或两个字母符号表达，大写字母表示孔而小写字母表示轴。这样基本尺寸为45毫米的一个孔和轴配合规格可能是45H8/g7。
Twenty standard grades of tolerances are provided, called IT01, IT0, IT1~18, providing numerical values for each nominal diameter, in arbitrary steps up to 500mm (for example 0~3, 3~6,6~10, ......, 400~500 mm).
ISO规定了二十种标准的公差等级，称之为IT01，IT0，IT1~18，给在直至500毫米强行分段(例如0~3，3~6，6~10, ......, 400~500毫米)中的公称直径提供具体数值。
The value of the tolerance unit, i, for grades 5~16 isWhere i is in microns and D in millimeters.
对5-16级而言，公差单位i的值可用下式计算这里i的单位是微米，而D的单位是毫米。
Standard shaft and hole deviations similarly are provided by sets of formulas, however, for practical application, both tolerances and deviations are provided in three sets of rather complex tables.
标准的轴和孔偏差同样都由若干公式提供?然而对实际应用，公差和偏差都在三张相当复杂的表格中规定了。
Additional tables give the values for basic sizes above 500 mm and for “Commonly Used Shafts and Holes” in two categories—“General Purpose” and “Fine Mechanisms and Horology”.
对基本尺寸大于500毫米和在“一般用途”和“精密机械和钟表”两个类别中的“常用的轴和孔”而言，由附加的表格给出数值。
