The term division of labor has, from long usage, become associated in the public mind with manual processes. But productive labor is, in general, bot… - Dexter S. Kimball

There is another and very important ground for standardization and that is the desirability of having parts interchangeable. Standards of exchange have long been in general use, and these have, most usually, been fixed with a view to convenient use rather than on a scientific basis. The units of weight and measure are examples of this form of standard. They may not even be the most logical, or most convenient, but once established they can, in general, be changed only by slow degrees, if at all.

By standardization is meant the reduction of any one line to fixed types and sizes. Thus in the case of the manufacturer of shoes he selects a few types that, in his opinion, will find favor in the market. But each foot is not measured and a shoe of the required type made to these measurements. A limited number of sizes of each type is manufactured, these sizes being selected, by previous experience, so that any average man can find a pair that will fit him. The same holds true for the case of electric motors discussed above, and in fact for the entire field of manufactured products.

Specialization, as has been noted, is the confining of human activity to a limited field. In industrial work this means the limitation of an enterprise to a portion of the field and to the production of a limited line of products. But even when the line of products is limited, there are usually many types that are possible in that line and an infinite number of sizes of any one type. Thus suppose a manufacturer specializes in the manufacture of men's shoes. Here there is no limit to the types that may be produced and no limit to the number of sizes of any type since no two feet are exactly alike. Again a manufacturer may specialize on the production of motors between the sizes, say, of one-half horse-power and twenty horse-power. Here again many types are possible and an infinite number of sizes for each type. But it has been shown that one of the essentials of cheap production is quantity, and for a given total output the greatest number of each element entering into the product is secured when the numbers of types and sizes are a minimum.