What are standards? specifications? codes?
A standard can be defined as a test method, definition, or recommended practice regarding manufacturing, testing, dimensions, and/or certification of raw materials and finished goods. The intent in creating a standard is to produce goods that are safe and reliable. Standards are usually created by organizations that are purposed for that activity. The terms standard, specification, and code are often used interchangeably.
Specification. A specification is a form of standard, which precisely states a set of requirements to be satisfied. These requirements might be chemical composition, mechanical properties, or any other requirement that is necessary to develop the quality and reliability of an end product. 
Code. The word “code" is a term of much broader meaning than either specification or standard and can best be described as a set of rules established by a recognized authority such as the US federal government's Code of Federal Regulations (CFR), and the American Society of Mechanical Engineers' (ASME), Boiler and Pressure Vessel Code. In adopting the rules that make up the various codes, consideration is generally based on health, safety, and environmental protection. The code-formulating bodies, in addition to writing their rules, usually adopt standards and specifications either in whole or in part to become a part of the code. 
 Adapted from the Steel Founders of America http://www.sfsa.org/sfsa/buyrord3.php
 The structure and content of this guide is based on the guide, Standards & Specifications: A How-To Guide, authored by Lorriw Pellack at Iowa State University.
Why? How? Historical
Why? Standards are important for safety, reliability, quality, ease of use, interchangeable parts; and consistency of products and processes across international borders. Standards are written for, but not limited to raw materials; manufactured products; methods of analysis, such as chemical, electrical, or mechanical; nondestructive testing; units of measure, such as time, distance, or mass; information privacy issues; environmental considerations; manufacturing processes; etc. Internationally accepted standards facilitate international trade.
How are standards created? Standards Development Organizations (SDO's) are composed of individuals from public and private industry, government and non-governmental organizations. Standards organizations meet on a regular basis to update existing standards and write new ones in response to new technologies, changes in laws, regulations, safety issues, performance criteria, etc. The typical standard is updated every 5 years.
What sparked the creation of standards in the first place? As societies entered the industrial age, the use of materials increased exponentially. Assessment of material quality by the craftsman became increasingly difficult in particular in the manufacture of steel. The discipline of engineering provided a scientific means of testing material quality; craftsmen who were not yet accustomed to the new materials and the skills needed to verify quality soon adapted the tools and methods required to make those assessments. The manufacture of steel became subject to disagreement between the steel mills and the railroads, when it was discovered that steel failed under stress due to insufficient material quality and heat treatment. The American Society of Testing & Materials formed from the participants who created the standards for manufactured steel. Any manufacturer who could comply with the new standards could participate in the market and thus steel manufacturing that satisfied the needs of the railroad and other industries grew as a result. Nearly every type of material and manufactured good from asphalt to zippers is governed by any number of relevant standards.
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