Articles related to GD&T symbol rules and walk-through examples of GD&T Symbols and their uses
"Why doesn’t Rule #1 apply to the straightness of a Derived Median Line?" In this article, we look at both surface straightness and straightness of a feature of size to understand why Derived Median Line Straightness overrules Rule #1 of GD&T.
The slope modifying symbol is placed with a value to indicate that this value is controlled as a slope, or a “flat taper.” The value listed with the symbol is the ratio of the height change to length change.
The conical taper symbol is placed with a dimension value to indicate that the value is controlled as a standard taper. The value listed with the symbol is the ratio of the diameter change to length change.
The Arc Length symbol, also known as the Arc Modifying symbol, is placed above a value to indicate that the arc’s length is being dimensioned on a curved outline.
A parting line is the location where separate parts of a mold or die come together. If the parting line is not dimensioned on the drawing, the location of the parting line is up to the manufacturer’s discretion.
The dimension origin symbol is used to indicate where a dimension must be measured from. This symbol is used in place of a dimensional arrow leader to indicate the origin for measurement.
The depth symbol is used to indicate a measurement from the bottom of a feature to the outer surface of a part.
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.