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ASME Y14.5 is a standard published by the American Society of Mechanical Engineers (ASME) to establish rules, symbols, definitions, requirements, defaults, and recommended practices for stating and interpreting Geometric Dimensions and Tolerances (GD&T). [1]
BS 8888 is the British standard developed by the BSI Group for technical product documentation, geometric product specification, geometric tolerance specification and engineering drawings. [ 1 ] History
The ISO 128 replaced the previous DIN 6 standard for drawings, projections and views, which was first published in 1922 and updated in 1950 and 1968. ISO 128 itself was first published in 1982, contained 15 pages and "specified the general principles of presentation to be applied to technical drawings following the orthographic projection methods".
Example of true position geometric control defined by basic dimensions and datum features. Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating engineering tolerances via a symbolic language on engineering drawings and computer-generated 3D models that describes a physical object's nominal geometry and the permissible variation thereof.
In mechanical engineering, limits and fits are a set of rules regarding the dimensions and tolerances of mating machined parts if they are to achieve the desired ease of assembly, and security after assembly - sliding fit, interference fit, rotating fit, non-sliding fit, loose fit, etc.
Engineering fits are generally used as part of geometric dimensioning and tolerancing when a part or assembly is designed. In engineering terms, the "fit" is the clearance between two mating parts, and the size of this clearance determines whether the parts can, at one end of the spectrum, move or rotate independently from each other or, at the other end, are temporarily or permanently joined.
The standard (size) tolerances are divided into two categories: hole and shaft. They are labelled with a letter (capitals for holes and lowercase for shafts) and a number. For example: H7 (hole, tapped hole, or nut) and h7 (shaft or bolt). H7/h6 is a very common standard tolerance which gives a tight fit.
When shearing a sheet, the typical tolerance is +0.1 inch or −0.1 inch, but it is feasible to get the tolerance to within +0.005 inch or −0.005 inch. While shearing a bar and angle, the typical tolerance is +0.06 inch or −0.06 inch, but it is possible to get the tolerance to +0.03 inch or −0.03 inches.