Metric Ball Screws

{flickr|100|campaign} Metric Ball Screws is the title given to those ball screw assemblies that have accuracy classifications determined using the metric system. Occasionally the measurement system is irrelevant, and ball screws which have identical accuracy levels can be categorised using either the metric system or the imperial system. However in some cases metric ball screws are more precise inch ball screws, which is the title used for those ball screws identified using the imperial system.
Levels of accuracy are the most important aspect of many ball screws, especially metric ball screws. For those who wish to purchase a ball screw assembly for their mechanism, the load levels and accuracy levels are aspects that will be fundamental in their choice. In previous centuries in Europe and America, the imperial units were the only measurement standards available. Typical imperial units are inches, feet, yards, pounds etc. However imperial measurement has a large disadvantage in that it does not have a single number as its base. In other words there are 12 inches in a foot and only 3 feet in a yard. The imperial system is therefore inconsistent, and cannot easily be represented using decimal numbers. Despite this, the imperial system is currently the accepted measurement system in the United States.
In the rest of the world the metric system is common|In much of the western world the metric system is universally applied|In other parts of the world the metric system is frequently used|The metric system is currently used outside of the United States}, and is is laid out in groups of ten, which means that is has measurements that can simply be converted to decimals. Units of length, which are important for accuracy in metric ball screws, are expressed in millimetres, centimetres and metres. As far as ball screws are concerned, it is not really feasible to express very high levels of precision using the imperial measurement approach. If we take instrument quality ball screws, which are samples of metric ball screws, may have levels of accuracy 250 nanometres per centimetre. A nanometre is 10-9 of a metre, or 0.000000001m, and 250nm is 0.00000025m. It is obvious that this figure does not lends itself to representation with the imperial measurement system, and therefore metric ball screws typically incorporate very precise instruments.