This Section establishes the symbols for specifying geometric characteristics and other dimensional requirements on engineering drawings. Symbols shall be of sufficient clarity to meet the legibility and reproducibility requirements of ASME Y14.2M. Symbols shall be used only as described herein.
- Use of notes to supplement symbols
- Geometric characteristic symbols
- Datum feature symbol
- Datum target symbol
- Basic simension symbol
- Material condition/Boundary symbols
- Projected tolerance zone symbol
- Diameter and radius symbols
- Reference symbol
- Arc length symbol
- Statistical tolerancing symbol
- Between symbol
- Counterbore symbol
- Spotface symbol
- Depth symbol
- 3.3.16 Square symbol
- 3.3.17 Dimension origin symbol
- 3.3.18 Taper and slope symbols
- 3.3.19 All around symbol
- 3.3.20 Free-state symbol
- 3.3.21 Tangent plane symbol
- 3.3.22 Unequally disposed profile symboll
- 3.3.23 Continuous feature symbol
- 3.3.24 Independency symbol
- 3.3.25 All-over symbol
- 3.3.26 Datum translation symbol
- 3.3.27 Movable datum target symbol
- Surface Texture Symbols
- 3.3.29 Symbols for limits and fits
- 3.3.30 Datum reference frame symbol
Use of notes to supplement symbols
Situations may arise where the desired geometric requirements cannot be completely conveyed by symbology. In such cases, a note may be used to describe the requirement, either separately or to supplement a geometric symbol. See Figs. 6-16, 6-17, and 7-54.
Geometric characteristic symbols
The symbolic means of indicating geometric characteristics are shown in Fig. 3-1.
Datum feature symbol
The symbolic means of indicating a datum feature consists of a capital letter enclosed in a square or rectangular frame and a leader line extending from the frame to the feature, terminating with a triangle. The triangle may be filled or not filled. See Fig. 3-2. Letters of the alphabet (except I, O, and Q) shall be used as datum identifying letters. Each datum feature of a part requiring identification shall be assigned a different letter. When datum features requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series (AA through AZ, BA through BZ, etc.) shall be used and enclosed in a rectangular frame. Where the same datum feature symbol is repeated to identify the same feature in other locations of a drawing, it need not be identified as reference. The datum feature symbol is applied to the feature surface outline, extension line, dimension line, or feature control frame as follows:
(a) placed on the outline of a feature surface, on an extension line of the feature outline, clearly separated from the dimension line, when the datum feature is the surface itself, or on a leader line directed to the surface. On 2D orthographic drawings where the datum feature is not on the visible surface, the leader line may be shown as a dashed line. See Fig. 3-3.
(b) placed on the dimension line or an extension of the dimension line of a feature of size when the datum is an axis or center plane. If there is insufficient space for the two arrows, one of them may be replaced by the datum feature triangle. See Figs. 3-4, illustrations (a) through
(c), (f), and (h); 4-33; and 4-35, illustrations (c) and (d). (c) placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is an axis. For digital data files, the triangle may be tangent to the feature. See Fig. 3-4, illustrations (e) and (g).
(d)placed on the horizontal portion of a dimension leader line for the size dimension. See Figs. 3-4, illustration (d); 4-33; and 4-35, illustrations (a) and (b).
(e) placed above or below and attached to the feature control frame. See para. 3.4.6 and Figs. 3-5 and 3-27. (f) placed on a chain line that indicates a partial datum feature. See Fig. 4-27.
Datum target symbol
The symbolic means of indicating a datum target shall be a circle divided horizontally into halves. The lower half contains a letter identifying the associated datum, followed by the target number assigned sequentially starting with 1 for each datum. See Figs. 3-6 and 4-48. A radial line attached to the symbol is directed to a target point, target line, or target area, as applicable. See para. 4.24.1. Where the datum target is an area, the size and shape of the area (true geometric counterpart) is entered in the upper half of the symbol; otherwise, the upper half is left blank. If there is not sufficient space within the compartment, the size and shape of the area may be placed outside and connected to the compartment by a leader line terminating with a dot. See Figs. 3-6 and 4-42.
Datum Target Points
A datum target point is indicated by the target point symbol, dimensionally located in a direct view of the surface. Where there is no direct view, the point location is dimensioned on two adjacent views. See Fig. 3-7.
Datum Target Lines
A datum target line is indicated by the datum target point symbol on an edge view of the surface, a phantom line on the direct view, or both. See Fig. 3-8. Where it is necessary to control the length of the datum target line, its length and location are dimensioned.
Datum Target Areas.
Where it is determined that an area or areas of contact is necessary to assure establishment of the datum (that is, where spherical or pointed pins would be inadequate), a target area of the desired shape is specified. The datum target area is indicated by section lines inside a phantom outline of the desired shape, with controlling dimensions added. The diameter of circular areas is given in the upper half of the datum target symbol. See Fig. 3-9, illustration (a). Where it becomes impractical to delineate a circular target area, the method of indication shown in Fig. 3-9, illustration (b) may be used.
Basic simension symbol
The symbolic means of indicating a basic dimension shall be as shown in Fig. 3-10.
Material condition/Boundary symbols
The symbolic means of indicating “at maximum material condition” or “at maximum material boundary,” “at least material condition” or “at least material boundary” shall be as shown in Figs. 3-11 and 4-5.
Projected tolerance zone symbol
The symbolic means of indicating a projected tolerance zone shall be as shown in Figs. 3-11, 7-21, and 7-22.
Diameter and radius symbols
The symbols used to indicate diameter, spherical diameter, radius, spherical radius, and controlled radius shall be as shown in Fig. 3-11. These symbols shall precede the value of a dimension or tolerance given as a diameter or radius, as applicable. The symbol and the value shall not be separated by a space.
The symbolic means of indicating a dimension or other dimensional data as reference shall be by enclosing the dimension (or dimensional data) within parentheses. See Figs. 2-3 and 3-11. In written notes, parentheses retain their grammatical interpretation unless otherwise specified. When it is necessary to define dimensions or dimensional data as reference in a note, the term “REFERENCE” or abbreviation “REF” shall be used.
Arc length symbol
The symbolic means of indicating that a dimension is an arc length measured on a curved outline shall be as shown in Fig. 3-11. The symbol shall be placed above the dimension and applies to the surface nearest the dimension.
Statistical tolerancing symbol
The symbolic means of indicating that a tolerance is based on statistical tolerancing shall be as shown in Fig. 3-11. If the tolerance is a statistical geometric tolerance, the symbol shall be placed in the feature control frame following the stated tolerance and any modifier. See Fig. 3-12. If the tolerance is a statistical size tolerance, the symbol shall be placed adjacent to the size dimension. See Fig. 3-13.
The symbolic means of indicating that a tolerance or other specification apply across multiple features or to a limited segment of a feature between designated extremities is shown in Figs. 3-11, 3-14, 8-6, and 8-7. The leader from the feature control frame is directed to the portion of the feature to which that tolerance applies. In Fig. 3-14, for example, the tolerance applies only between G and H. G and H may be points, lines, or features.
It uses a symbolic language rather than words on engineering drawings that explicitly describes nominal geometry and its allowable variatioThe symbolic means of indicating a counterbore shall be as shown in Figs. 1-37 and 3-15. The symbol shall precede, with no space, the dimension of the counterbore.n. The GD&T system has a strong mathematical base.
The symbolic means of indicating a spotface shall be as shown in Figs. 1-41 and 3-15. The symbol shall precede, with no space, the dimension of the spotface.
The symbolic means of indicating a countersink shall be as shown in Fig. 3-16. The symbol shall precede, with no space, the dimensions of the countersink.
The symbolic means of indicating that a dimension applies to the depth of a feature is to precede that dimension with the depth symbol, as shown in Fig. 3-17. The symbol and the value are not separated by a space.
The symbolic means of indicating that a single dimension applies to a square shape shall be to precede that dimension with the square symbol, as shown in Figs. 3-11 and 3-18. The symbol and the value shall not be separated by a space.
Dimension origin symbol
The symbolic means of indicating that a toleranced dimension between two features originates from one of these features and not the other shall be as shown in Figs. 2-5, 3-11, and 3-19.
Taper and slope symbols
The symbolic means of indicating taper and slope for conical and flat tapers shall be as shown in Figs. 2-20 and 2-21. These symbols shall be shown with the vertical leg to the left.
All around symbol
The symbolic means of indicating that a profile tolerance applies to surfaces all around the true profile in the view shown is a circle located at the junction of the leader from the feature control frame. See Figs. 3-11, 3-20, and 8-12.
For features or datum feature references subject to free-state variation as defined in para. 5.5, the symbolic means of indicating that the geometric tolerance or datum feature applies in its “free state” is shown in Figs. 3-1 and 3-21. When the symbol is applied to a tolerance in the feature control frame, it shall follow the stated tolerance and any modifier. When the symbol is applied to a datum feature reference, it shall follow that datum feature reference and any modifier.
Tangent plane symbol
The symbolic means of indicating a tangent plane shall be as shown in Fig. 3-11. The symbol shall be placed in the feature control frame following the stated tolerance as shown in Fig. 6-18. Also, see paras. 1.3.45 and 6.5.
Unequally disposed profile symbol
This symbol indicates a unilateral or unequally disposed profile tolerance. The symbol shall be placed in the feature control frame following the tolerance value as shown in Figs. 3-11 and 8-1 through 8-3 and para. 126.96.36.199.
Continuous feature symbol
This symbol indicates a group of two or more interrupted features as a single feature. See Figs. 2-8 through 2-10 and 3-11 and para. 2.7.5.
symbol indicates that perfect form of a feature of size at MMC or at LMC is not required. The symbol shall be placed next to the appropriate dimension or notation. See Fig. 3-11 and para. 2.7.3.
This symbol indicates that a profile tolerance or other specification shall apply all over the three-dimensional profile of a part. See Figs. 3-11, 3-20, and 8-8 and para. 188.8.131.52.
Datum translation symbol
This symbol indicates that a datum feature simulator is not fixed at its basic location and shall be free to translate. See Figs. 3-11, 4-19, and 4-32, illustration (b), and para. 4.11.10.
Movable datum target symbol
This symbol indicates that a datum target is not fixed at its basic location and is free to translate. See Figs. 3-22, 4-47, and 4-49 and para. 4.24.6
Surface Texture Symbols
For information on the symbolic means of specifying surface texture, see ASME Y14.36M.
Symbols for limits and fits
For information on the symbolic means of specifying metric limits and fits, see para. 2.2.1.
Datum reference frame symbol
The datum reference frame symbol shall consist of the X, Y, and Z coordinate labels applied to the axes of the datum reference frame. See Figs. 4-1 and 4-2.