Chapter 1 Geometric Dimensioning and Tolerancing Essentials 7 Copyright Goodheart-Willcox Co., Inc. The early history of GD&T is vague, but historians recognize the work of Stanley Parker and committees of the British Admiralty as the origin of what has become GD&T. Parker was involved in munitions manufacturing as an employee at the Royal Torpedo Factory in Scotland in 1938, and later at the Naval Ordnance Gauge Factory in England. While working at the Royal Torpedo Factory, Parker developed the theory of positional tolerancing. Parker’s work focused on dimensioning and tolerancing, or re-dimensioning and tolerancing, the geometry on drawings of naval weapons to increase production of the weapons by various contractors. Parker’s text, Notes on Design and Inspection of Mass Production Engineering Work, published in 1940, provides an early account of geometrical methods in dimensioning and tolerancing. The principles of this document served as a guide for future dimen- sioning and tolerancing manuals and standards. The British Standards (BS) document BS 308:1953, titled Engineering Drawing Office Practice, for which Parker took part in authoring, was the first BS 308 standard to include geometrical methods in dimension- ing and tolerancing. Parker’s Drawings and Dimensions text, published in 1956, inter- preted the principles upon which the dimensioning and tolerancing methods in BS 308:1953 were based. Early geometric dimensioning and tolerancing records focused on describing standards and practices through written descriptions and traditional drafting notation. The symbols and systems that we associate today with GD&T evolved over time, as detailed in various GD&T standards and standard revisions. GD&T Standards A standard is a set of technical definitions and guidelines that establishes requirements for designers and manufacturers. Standards are developed by professional organi- zations, companies, and government agencies. Companies involved in engineering and design adopt drafting standards in order to follow recognized industry practices. Incorporating and maintaining standardized practices allows companies to improve efficiency by reducing errors and lowering costs. Standards are defined as voluntary because they serve as guidelines, but a standard becomes a required document when specified in a contract between businesses. A code is a standard that has been adopted by a governmental body and is enforced by law. GD&T standards grew from basic articles describing the control of geometric characteristics such as position, straightness, and flatness. These articles were writ- ten according to understood design and drafting practices of the time and evolved to more complex documents intended to define the exact meaning of geometric charac- teristics. Early GD&T standards included the following: • The BS 308:1953 Engineering Drawing Office Practice standard and later revisions • Technical papers and documents published in 1945 and later by the Society of Automotive Engineers (SAE), now known as SAE International • The ORD 30-1-7 Standard Dimensioning and Tolerancing standard published by the US Army Ordnance Corps (1946) • The MIL-STD-8 Dimensioning and Tolerancing standard published by the US military (1949) • The ASA Y14.5 American Drafting Standards Manual, Section 5: Dimensioning and Notes standard published by the American Standards Association (1957) ASME and the International Organization for Standardization (ISO) publish the pri- mary GD&T standards that designers and manufacturers reference today. ASME and ISO dimensioning and tolerancing standards were developed over time from early GD&T principles and multiple revisions of earlier standards. In general, ASME standards apply to work done in the United States, and ISO standards are primarily used in Europe. However,