英语翻译Machine parts are manufactured so they are interchangeab

英语翻译
Machine parts are manufactured so they are interchangeable.
In other words,each part of a machine or mechanism is made
to a certain size and shape so it will fit into any other
machine or mechanism of the same type.To make the part
interchangealbe,each individual part must be made to a size
that will fit the mating part in the correct way.It is not
only impossible,but also impractical to make many parts to
an exact size.
This is because machines are not perfect,and the tools
become worn.A slight variation from the exact size is
always allowed.The amount of this variation depends on the
kind of part being manufactured.For example,a part might
be made 6 in.long with a variation allowed of 0.003 (three
-thousandths) in,above and below this size.Therefore,the
part could be 5.997 in.to 6.003 in.and still be the
correct size.These are known as the limits.The difference
between upper and lower limits is called the tolerance.
When the tolerance is in both directions from the basic
size,it is known as a bilateral tolerance(plus and minus).
Sometimes the limit is allowed in only one direction.This
is known as unilateral tolerance.
Forexample a hole may have to be 2in.minus 0.000in.,or
plus 0.005 smaller than 2 in.but can he as large as 2.005
in.
目前没分了 以后补上50分

机械零部件的制造,以便他们可以互换.
换句话说,每一个机器或机制的一部分是由
在一定的大小和形状,以便它适合任何其他
机或相同类型的机制.为了使部分
interchangealbe,每个部分必须作出的大小
将适合在正确的方式交配的一部分.这不是
只是不可能,而且不切实际,使许多地区
精确的尺寸.
这是因为机器不是完美的,和工具
陈旧.从精确的尺寸略有变化
始终允许.这一变化量取决于
正在生产的部分实物.例如,可能有部分
作出的允许6英寸长0.003,变异（3
-千分之一）的,上面和下面这个大小.因此,
部分可5.997英寸到6.003英寸,仍然是
正确的大小.这些被称为限制.不同之处
上限和下限之间,是所谓的容忍.
当宽容是从两个方向的基本
尺寸,它被称为双边公差（加号和减号）.
有时候,限制只允许在一个方向.这
被称为单方面的宽容.
例如采取了一个洞,可能要2英寸减去0.000英寸,或
加0.005小于2英寸,但他可以作为大,2.005
英寸