What is GD&T (Geometric Dimensioning and Tolerancing)?

GD&T (Geometric Dimensioning and Tolerancing) is a set of symbols used in design. These symbols are based on international standards ASME and ISO. Both standards use almost the same symbols. There are only up to 20% differences between them. Therefore, a person who is familiar with any of the ISO or ASME standards will not have much difficulty using GD&T.

GD&T starts with the designer designing a part. However, this design needs to be dimensioned and tolerated so that the person or team that will produce the part can produce it correctly and to the desired quality. Therefore, the designer needs to know the meanings, usage areas and interpretation of many GD&T symbols.

Then comes production. Production must also know what these symbols used in design mean so that it can physically produce the desired design.

And finally the quality team comes. The quality team needs to check the manufactured part according to the symbols shown in the design. Therefore, the quality team also needs to be familiar with GD&T.

Although GD&T is an important engineering language that makes serious contributions to product feasibility and directly affects product costs when applied correctly, it is not taught as a separate course in universities, but is only briefly covered in mechanical engineering classes. For this reason, when our young people enter business life, they have difficulty reading, creating and interpreting technical drawings. Most companies direct their new employees to GD&T training in order to fill this gap.