The International System of Units (SI)

and its relationship to U.S. customary units

ENGINEERING STANDARDS

Appendix 4

A. Background

The intimate relationship between units of measurement and engineering standards is recognized in Public Law 90-472, which states that "the Secretary shall give full consideration to the advantages, disadvantages, and problems associated with possible changes in either the system of measurement units or the related dimensional and engineering standards currently used in the United States." Further, PL 90-472 authorizes the Secretary of Commerce "to study the feasibility of retaining and promoting by international use of dimensional and engineering standards based on the customary measurement units of the United States." In the survey of engineering standards, the study has revealed that the measurement system is only one factor involved in the promotion of our national standards for international use. A factor that appears to be at least equally important is participation in committees, subcommittees, and working groups of international standardizing organizations. Currently, U.S. participation in such committees ranges from none to very high, depending on the industry concerned.

An understanding of the standards setting process throughout the world is helpful to an appreciation of the significance of the dynamic environment of today.

Wherever a multiplicity of practices is both possible and likely to occur, group cooperation for the achievement of some desirable social goal may require the acceptance, by the members of the group, of some joint decision to use one or a limited number of the possible alternatives. When the activities involved relate to social behavior the agreements (standards) are called laws. When related to religious behavior they are canons. And when related to manufacturing, testing, measurement practices and conventions, properties and performance of materials, or to the performance or characteristics of things, they are variously called standards of practice, code regulations, or conventions. All of these latter are commonly lumped together under the term "engineering standards."

The essential ingredients for arriving at such standards are:

(1) A set of alternatives,

(2) A method for agreeing upon a selection to be used,

(3) A group which agrees to abide by the selection, and
(4) Means for insuring compliance.

History is replete with chronicles of struggles to impose standards upon a reluctant society (e.g., crusades) or to unify a disparate set (e.g., conflicts of law). Engineering standards are no exception. Once set and embodied in our technology, products and applications, they may be difficult to change. The controversies over metrication in times past have revolved mostly around the standards issue, although often disguised as a language problem.

To return from this historical digression, the number of alternatives in any specific situation may range from a minimum of two (e.g., right or left handed screw threads, or right or left side of road for driving) to an unlimited number ranging over all the products and conventions in which our society is involved – for example, all possible sizes for shoes, hats, clothes, electrical outlets and plugs, doors, windows, bricks, tires, wires, drills, screws.

The cooperating group may extend from a buyer and a seller, to a company, to an industry, to a nation or even to the whole world, which is the matter of immediate concern. This group also generally involves competing interests whose desires and goals for choices among alternatives may differ, as they do between producers, assemblers, consumers, or buyers and sellers. It may also include those who actually had no effective voice in the selection or agreement and may or may not feel bound to it, and some who do not choose to follow the agreement for selfish or unselfish reasons.

The decisions reached about the alternatives to be selected may be legally binding (i.e., mandatory) or voluntary, to be used at the will of the participants. Likewise, in this country as well as in others, the decisions (standards) may at times be propagated by one subgroup (such as producers or assemblers) and presented as an accomplished fact to another subgroup, such as consumers. Within the United States, standardization has been permissive and voluntary, with a few exceptions relating to standards based upon specific Federal, state or local legislation and concerned with health, safety or fraud. Other exceptions are regulations promulgated by the regulatory agencies such as the Federal Aviation Administration, Food and Drug Administration, or Federal Trade Commission.

The pattern of standards development has evolved into two main classes. At the industry level, standards are developed by materials and parts producers and device assemblers and presented to the ultimate consumer in the market place. Alternatively, the standards may be promulgated as procurement specifications by a buyer that is sufficiently large and important to have the standards met -for example, the Federal Government. In this connection it should be noted that when products are made to meet Federal Government specifications, others may also buy them and the specifications may become de facto national or even international standards through producer and consumer usage. A large fraction of these specifications has achieved this status. In fact, military and other federal specifications include more standards for consumer goods than those issued by all private or