机械类英语在线翻译 这学期学的机械专业英语，这东西实在学不懂，大家帮忙翻译一下，这是考试题，谢谢。

机械类英语在线翻译 这学期学的机械专业英语，这东西实在学不懂，大家帮忙翻译一下，这是考试题，谢谢。
Housings and other parts are often located in jigs and fixtures on a flat surface and holes. A workpiece resting on a flat surface will be definitely located by two holes which fit over two locating pins in the jig or fixture.
Heavy workpieces are usually located on retractable locating pins which are extended into the locating holes after the workpiece has been loaded on the flat surface.
One of the locating pins is usually of the diamond type to reduce the effect of a dimensional variation between the holes on the setting-up accuracy,As an example,a certain workpiece is located on two straight(cylindrical)pins.It will be assumed that the workpiece may be loaded and removed from the jig or fixture if there is no clearance between locating holes and pins and if the distance between the holes is the nominal value.To load workpiece in which the centre-to-centre distance L varies within the tolerance 2a,the corresponding clearance will have to be provided between one of the locating pins and its hole in the workpiece.Otherwise,only workpiece,in which the deviation of the distance L corresponds to the clearance between none pin and its hole,can be located on the two pins.
The position of the workpiece,in the direction of a line passing through the hole centres, is fully determined by one locating pin.Angular location of the workpiece about the first pin is provided for by a second pin.
Therefore,if the second pin is of the diamond type,it will be possible to decrease the clearance between the diamond pin and hole in a direction important for proper location, i.e.,to increase the angular co-ordination accuracy.