| actual local size |
A size dimension that indicates the measurement of a section of a feature that is formed by an intersecting imaginary plane. Also called cross-sectional dimension, actual local size is often measured with calipers or a micrometer. |
| actual mating envelope |
AME. A geometrically perfect shape that is an imaginary shape that best fits around a feature. AME can be established by inspecting a feature's height and cross-sectional dimensions. |
| caliper |
A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. The jaws can measure both internal and external features. |
| circular runout |
A two-dimensional geometric tolerance that controls the form, orientation, and location of multiple cross sections of a cylindrical part as it rotates. Circular runout is a related tolerance. |
| circularity |
A two-dimensional form tolerance that describes the allowable variability in the shape and appearance of a circle. Also known as roundness, circularity is an individual tolerance. |
| concentricity |
A three-dimensional locational tolerance that describes the location of opposing points in cylindrical features with respect to a datum reference. Concentricity is a related tolerance. |
| coordinate measuring machine |
CMM. A sophisticated measuring instrument with a flat polished table and a suspended probe that measures parts in three-dimensional space. CMMs can measure using either contact or noncontact methods. |
| cross section |
A section of a feature that is formed by an intersecting imaginary plane. Any two-dimensional cross section of a feature should remain within two imaginary concentric circles to have circularity. |
| cross-sectional dimension |
A size dimension that indicates the measurement of a section of a feature that is formed by an intersecting imaginary plane. Also called actual local size, cross-sectional dimensions are often measured with calipers or a micrometer. |
| cylindricity |
A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a cylinder. Cylindricity is an individual tolerance. |
| dial indicator |
A measuring instrument with a contact point attached to a spindle and gears that move a pointer on the dial. Two opposing dial indicators can be used to measure the concentricity of a cylindrical feature. |
| functional gage |
A gage representing a worst case mating part that provides a simple pass/fail assessment of the inspected part. Functional gages often can quickly inspect several features at once. |
| height gage |
A measuring device with a column mounted on a base such as a granite surface plate, a unit that slides up and down, an indicator, and an arm that extends out. Height gages are used to measure vertical and other distances. |
| lobing |
Deviation from workpiece roundness. Circularity, cylindricity, and runout all restrict lobing on a cylindrical part. |
| maximum material condition |
MMC. The point at which a feature contains the greatest amount of material within its acceptable size limit. The smallest acceptable hole and the largest acceptable shaft are examples of MMC. |
| micrometer |
A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring assorted dimensions and features. |
| optical comparator |
A sophisticated measuring instrument that projects an image of a part onto a screen to compare the shape, size, and location of its features to the original. Also called optical projectors, they can measure both surface and profile features of either the length and width of a part but not the depth. |
| pin gage |
A type of gage available in a set and used to measure hole diameter. Pin gages are available in different ranges from .028 to 1.000 inch sizes (7.112 to 25.4 mm) in increments of 0.001 inch (0.025 mm). |
| plug gage |
A type of go/no-go gage in which two pins are located on opposite ends of a plug gage handle. A pin equal to the smallest allowable dimension acts as the go gage and a pin larger than the largest allowable dimension acts as the no go gage. |
| position |
A three-dimensional geometric tolerance that controls how much the location of a feature can deviate from its true position. Position is a related tolerance. |
| regardless of feature size |
RFS. A modifier indicating that the stated tolerance for a feature applies regardless of its actual size within an acceptable size limit. If RFS controls a location being inspected for position, that location should be inspected with a variable gage. |
| roundness machine |
A sophisticated inspection device with a precision spindle that measures various circular and cylindrical features. A roundness machine is necessary for inspecting such tolerances as circularity, cylindricity, circular runout, and total runout. |
| size dimension |
A dimension that indicates a linear measurement. Size dimensions are inspected first during part inspection. |
| tolerance zone |
An imaginary zone in which a part feature must be completely contained for the part to pass inspection. The tolerance zone contains the dimensions between the maximum and minimum limits of a feature's location. |
| total indicator reading |
TIR. The absolute value of the total deviation of a dial indicator's movement. TIR is calculated to inspect the total runout of a cylindrical part or the flatness of a prismatic part. |
| total runout |
A three-dimensional geometric tolerance that controls the form, orientation, and location of the entire length of a cylindrical part as it rotates. Total runout is a related tolerance. |
| vernier |
A type of scale consisting of two opposing line markings with different divisions. Vernier scales appear on both manual and digital calipers and micrometers. |