The “M” in Standards

Twisting measuring tape representing the metric system (SI units), which are reflected in standards by an M.

Regardless of industry, each standard has a unique designation, each component of which conveys its background. In these designations, numbers (and some letters) represent the developing committee. These come after the name of the standards developing organization (SDO), which, in the case of American National Standards, is accompanied by ANSI (e.g. ANSI/ASSE Z117.1-2022).

The letter “M” is present in some documents developed and published by the American Welding Society (AWS) or ASTM International. These documents contain M in their titles to distinguish between adherence through either U.S. customary units or SI units.

ASTM is an international organization that develops and publishes thousands of technical standards that serve the expanse of industries and occupations. Similarly, AWS, while specifically serving welders, supervisors, engineers, manufacturers, and numerous other professionals, has over 70,000 members worldwide, being composed of 22 districts of 250 sections and student chapters.

A welder following AWS D17.1M and safety practices with flying sparks.

The Unites States stands out from the rest of the world, especially when it comes to standardized systems. For systems of measurement, the US stands alone as the only industrial country that still uses inch-pounds units, while the rest have long adopted the metric system. For US-based SDOs writing standards intended for use both domestically and globally, there is a need for guidelines to be accessible through both systems of measurement, when applicable.

For this purpose, standards like ASTM E96/E96M-22a: Standard Test Methods for Water Vapor Transmission of Materials are presented as one document, but, as mentioned in the scope of that document, “the values stated in either SI units or inch-pound units are to be regarded separately as standard.” Therefore, adhering to ASTM E96 differs from ASTM E96M because the latter involves using SI units.

This same idea holds true in similarly designated AWS standards. In fact, some tables near the end of the AWS D17.1/D17.1M:2017 – Specification for Fusion Welding for Aerospace Applications document are split up by the usage of inches or millimeters (e.g. Table B.3 and Table B.3M).

However, accommodating metric units goes beyond being accessible by various users. The AWS Metrication Policy states, in part, “The AWS supports a timely transition to the use of SI units.” For the US welding industry, being able to reliably carry out unit conversions can be crucial for remaining competitive in international markets. AWS A1.1:2016 – Metric Practice Guide for the Welding Industry provides assurance in fulfilling this goal.

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