Geometric Dimension and Tolerance (GD&T)
is a framework for characterizing and imparting designing resistances. It utilizes emblematic language on designing drawings and PC created three-dimensional strong models that unequivocally depict ostensible math and its reasonable variety. It tells the assembling staff and machines what level of exactness and accuracy is required on each controlled component of the part. GD&T is utilized to characterize the ostensible (hypothetically great) math of parts and congregations, to characterize the suitable variety in structure and conceivable size of individual highlights, and to characterize the permissible variety between highlights.
Measurement details characterize the ostensible, as-displayed or as-expected math. One model is a fundamental measurement.
Resistance details characterize the reasonable variety for the structure and perhaps the size of individual highlights, and the admissible variety in direction and area between highlights. Two models are direct measurements and highlight control outlines utilizing a datum reference (both appeared previously).
There are several standards available worldwide that describe the symbols and define the rules used in GD&T. One such standard is American Society of Mechanical Engineers (ASME) Y14.5. This article is based on that standard, but other standards, such as those from the International Organization for Standardization (ISO), may vary slightly. The Y14.5 standard has the advantage of providing a fairly complete set of standards for GD&T in one document. The ISO standards, in comparison, typically only address a single topic at a time. There are separate standards that provide the details for each of the major symbols and topics below (e.g. position, flatness, profile, etc.).