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| Aligned Dimension | A system of dimensioning which requires all numerals, figures, and notes to be aligned with the dimension lines so that they may be read from the bottom (for horizontal dimensions) and from the right side (for vertical dimensions). |
| American National Standards Institute (ANSI) | 1. A private, non-profit organization that coordinates the development and use of voluntary consensus standards in the United States. 2. The acronym for the America National Standards Institute. |
| American Society of Mechanical Engineers (ASME) | 1. A professional engineering organization that is known for setting codes and standards for mechanical devices in the United States. ASME drawing standards are found in the Y-14M publications. 2. The acronym for the American Society of Mechanical Engineers. |
| Arrowheads | Arrowheads are used to indicate the end of a dimension line or leader. |
| Baseline Dimensioning | System of dimensioning in which all dimensions are placed from a datum and not from feature to feature. Also referred to as Datum Dimensioning. |
| Chain Dimensioning | Also known as point-to-point dimensioning where dimensions are established from one point to the next. |
| Datum | A theoretically exact point, axis, or plane derived from the true geometric counterpart of a specific datum feature. The origin from which the location, or geometric characteristic of a part feature, is established. |
| Datum Dimension | A dimensioning system where each dimension originates from a common surface, plane, or axis. Also known as baseline dimensioning. |
| Dimension | A measurable extent, such as the three principal dimensions of an object is width, height, and depth. Length and thickness are not used because they cannont be applied in all cases. The front view of an object shows only the height and width and not the depth. In fact, any one view of a three-dimensional object can show only two dimensions, the third dimension will be found in an adjacent view. |
| Dimension Lines | Lines that are thin lines capped with arrowheads, which may be broken along their length to provide space for the dimension numerals. |
| Dual Dimensions | Where alternate units are displayed within the same dimension (both metric and standard dimensions can shown at the same time). |
| Extension Lines | Thin lines used to establish the extent of a dimension. Extension lines begin with a short space from the object and extend to about .125 inches past the last dimension line. Extension lines may cross object lines, center lines, hidden lines, and other extension lines, but may not cross dimension lines. |
| General Notes | Notes placed separate from the views; relate to the entire drawing. |
| Leaders | Lines that are thin and used to connect a specific note to a feature. |
| Least Material Condition (LMC) | The smallest size limit of an external feature and the largest size limit of an internal feature. |
| Limits of Dimension | The largest and smallest possible boundaries to which a feature may be made as related to the tolerance of the dimension. |
| Local Notes | Connected to specific features on the views of the drawing. Also known as annotations. |
| Maximum Material Condition (MMC) | The largest size limit of an external feature and the smallest size limit of an internal feature. |
| Bilateral Tolerance | A tolerance in which variation is permitted in both directions from the specified dimension. |
| Location Dimension | A location dimension that defines the relationship of features of an object. |
| Nominal Size | The designation of the size established for a commercial product. |
| Reference Dimension | A dimension, usually without a tolerance, used for information purposes only. A reference is a repeat of a given dimension or established from other values shown on a drawing. Reference dimensions are enclosed in ( ) on the drawing. |
| Size Dimensions | Placed directly on a feature to identify a specific size or may be connected to a feature in the form of a note. |
| Tolerance | The total permissible variation in a size or location dimension. |
| Unidirectional Dimension | A dimensioning system which requires all numerals, figures, and notes to be lettered horizontally and be read from the bottom of the drawing sheet. |
| Unilateral Tolerance | A tolerance in which variation is permitted in only one direction from the specified dimension. |
