Geometric dimensioning and tolerancing

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.

GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, the allowable variation in size, form, orientation, and location of individual features, and how features may vary in relation to one another such that a component is considered satisfactory for its intended use.

There are separate standards that provide the details for each of the major symbols and topics below (e.g. position, flatness, profile, etc.).

While little is known about Parker's life, it is known that he worked at the Royal Torpedo Factory in Alexandria, West Dunbartonshire, Scotland.

Unequal bilateral and unilateral tolerances for profile are specified by adding further information to clearly show this is what is required.

[2] GD&T can more accurately define the dimensional requirements for a part, allowing over 50% more tolerance zone than coordinate (or linear) dimensioning in some cases.

Proper application of GD&T will ensure that the part defined on the drawing has the desired form, fit (within limits) and function with the largest possible tolerances.

The American Society of Mechanical Engineers (ASME) provides two levels of certification: [4] Exchange of geometric dimensioning and tolerancing (GD&T) information between CAD systems is available on different levels of fidelity for different purposes: In ISO/TR 14638 GPS – Masterplan the distinction between fundamental, global, general and complementary GPS standards is made.