Articles related to GD&T symbol rules and walk-through examples of GD&T Symbols and their uses
The Spherical Diameter symbol is used to indicate that the Diameter is of a spherical, rather than circular, feature.
The diameter symbol is used to indicate that the size of a circular feature is being dimensioned using the diameter of that feature.
The Controlled Radius symbol is a variation of the Radius, and is used when the surface of the contour is required to be a "fair" curve.
The Spherical Radius is used to indicate that the Radius is of a spherical, rather than circular, feature.
The Square symbol is used to indicate a square feature on a drawing.
The Radius symbol is used when a circular feature is dimensioned using the radius length.
A countersink consists of a conical hole that is coaxial to a cylindrical hole, where the angle of the cone is determined by the fastener to be used. The purpose of a countersink is to allow a fastener, typically a flathead screw, to sit slightly below the surface of the part.
A spotface is a very shallow flat-bottomed cylindrical hole that is larger than and coaxial to another cylindrical hole. Its purpose is to provide a flat mounting surface for mating parts, such as washers or pan head screws.
The counterbore symbol is used on a drawing to indicate that a counterbore hole feature is required. A counterbore is a flat-bottomed cylindrical hole that is larger than and coaxial to another cylindrical hole.
The Tangent Plane Symbol is used in conjunction with GD&T surface controls to indicate that a specific control is applied to a theoretical tangent plane simulated by the high points of irregular tangible surface rather than the actual elements of the surface themselves.
The Free State Symbol is in used GD&T to indicate that a specific dimension and its associated tolerance are to be assessed in an unrestrained state.
The Projected Tolerance Symbol is in used GD&T to indicate the tolerance zone of a feature is to be assessed beyond the surface extents of the feature.
The Continuous Feature Symbol is used to indicate that a group of disjointed features or surfaces are to be considered as one continuous feature.
The Datum Target Symbol is used to define a specific point, line, or area to be used in order to establish a datum on a drawing.
The Envelope Requirement Symbol is used on ISO drawings to declare that size is to control form with respect to perfect form at MMC.
The Independency Symbol is used on drawings to declare that the requirement for perfect form at MMC or LMC is removed and the form tolerance may be larger than the size tolerance. This symbol only exists in the ASME Y14.5 standards, not the ISO GPS standards.
GD&T Rule #1, also known as the Envelope principle, states that the form of a regular feature of size is controlled by its “limits of size." Limits of size, or otherwise known as size tolerances, can be seen in many forms. A few of them are symmetric, unilateral, and bilateral.
The unequally disposed profile tolerance symbol is used to apply unilateral or unequal tolerance zones to a profile of a part.