## 14 geometric tolerances, can you distinguish them clearly?

Time：2022-07-26 17:23:04 / Popularity： / Source：

In production, if we misunderstand geometric tolerances marked on drawings, it will cause processing analysis, processing results and requirements to deviate, and even bring serious consequences. Today, let us systematically understand 14 geometrical tolerances.
Let's take a look at key points first. Following table is 14-item geometric tolerance symbols of international uniformity, which is very important.
 Tolerance Type Feature item Symbol With or without benchmark requirements Shape tolerance Shape Straightness No Flatness No Roundness No Cylindricity No Shape or position tolerance Contour Line profile Yes or No Face profile Yes or No Position tolerance Orientation Parallelism Yes Verticality Yes inclination Yes Position Degree of location Yes or No Coaxial (Concentricity) Yes Symmetry Yes Beat Round beat Yes Full beat Yes

## 01 Straightness

Straightness, commonly referred to as straightness, indicates that actual shape of linear elements on part maintains an ideal straight line. Straightness tolerance is maximum allowable variation from an actual line to an ideal line.
Example 1: In a given plane, tolerance zone must be in the area between two parallel straight lines at a distance of 0.1mm. Example 2: Mark Φ before tolerance value, tolerance zone must be within area of cylindrical surface with a diameter of 0.08mm. ## 02 Flatness

Flatness, which is commonly referred to as flatness, indicates actual shape of plane elements of part and maintains condition of ideal plane. Flatness tolerance is maximum allowable variation of actual surface from ideal plane.
Example: Tolerance zone is area between two parallel planes at a distance of 0.08mm.

## 03 Roundness

Roundness, commonly referred to as roundness, indicates that actual shape of circular element on the part is equidistant from its center. Roundness tolerance is maximum allowable variation between actual circle and ideal circle on same section.
Example: Tolerance zone must be on same normal section, and radius difference is area between two concentric circles with a tolerance value of 0.03mm. ## 04 Cylindricity

Cylindricity means that points on outline of cylindrical surface of part are kept equidistant from their axes. Cylindricity tolerance is maximum allowable variation of actual cylinder to ideal cylinder.
Example: A tolerance zone is area between two coaxial cylindrical surfaces with a radius difference of 0.1mm. ## 05 Line Profile

Line profile is condition of a curve of any shape on a given plane of a part that maintains its ideal shape. Line profile tolerance refers to allowable variation of actual profile of a non-circular curve.
Example: A tolerance zone is area between two envelopes enclosing a series of circles with a diameter of 0.04mm tolerance. Centers of circles lie on lines with theoretically correct geometry.

## 06 Face profile

Surface profile is condition of an arbitrary-shaped curved surface on a part that maintains its ideal shape. Surface contour tolerance refers to actual contour line of non-circular surface and allowable variation of ideal contour surface.
Example: Tolerance zone is between two envelopes enclosing a series of 0.02mm diameter spheres, centres of which should theoretically lie on the face of theoretically correct geometry. ## 07 Parallelism

Parallelism, which is commonly referred to as degree of parallelism, indicates condition that measured actual elements on part maintain an equidistant relative to reference. Parallelism tolerance is maximum allowable variation between actual orientation of measured feature and ideal orientation parallel to datum.
Example: If mark Φ is added before tolerance value, tolerance zone is within cylindrical surface with reference parallel diameter of Φ0.03mm. ## 08 Verticality

Perpendicularity, which is commonly referred to as degree of orthogonality between two elements, indicates that measured element on part maintains a correct 90° angle relative to reference element. Squareness tolerance is maximum allowable variation between actual direction of measured feature and ideal direction perpendicular to reference.
Example 1: Mark Φ is added before tolerance zone, then tolerance zone is perpendicular to cylindrical surface with a diameter of 0.1mm on reference plane. Example 2: Tolerance zone must lie between two parallel planes at a distance of 0.08mm and perpendicular to reference line. ## 09 Incline

Slope is correct condition for maintaining any given angle relative to orientation of two elements on a part. Slope tolerance is maximum allowable variation between actual orientation of feature being measured and ideal orientation at any given angle with respect to datum.
Example 1: Tolerance zone of measured axis is area between two parallel planes with a distance of 0.08mm and a theoretical angle of 60° with reference plane A. Example 2: Add mark Φ before tolerance value, then tolerance zone must be located in cylindrical surface with a diameter of 0.1mm. Tolerance zone should be parallel to plane B perpendicular to datum A and at a theoretically correct angle of 60° to datum A.

## 10 Position degrees

Position degree is exact condition of points, lines, surfaces and other elements on part relative to its ideal position. Position tolerance is maximum allowable variation in actual position of feature being measured relative to its ideal position.
Example: When mark SΦ is added in front of tolerance zone, tolerance zone is inner area of sphere with a diameter of 0.3mm. Position of center point of ball tolerance zone is theoretically correct dimension relative to datums A, B and C. ## 11 Coaxial (concentric) degrees

Concentricity, commonly referred to as coaxiality, indicates that measured axis on part is kept on same straight line relative to reference axis. Concentricity tolerance is allowable variation of actual axis being measured relative to reference axis.
Example: When tolerance value is marked, tolerance zone is area between cylinders with a diameter of 0.08mm. Axis of circular tolerance zone is aligned with datum.

## 12 Symmetry

Symmetry refers to state that the two symmetrical central elements on the part are kept in same central plane. Symmetry tolerance is allowable variation of symmetry center plane (or center line, axis) of actual feature from ideal symmetry plane.
Example: Tolerance zone is area between two parallel planes or straight lines with a distance of 0.08mm and symmetrically arranged with respect to reference center plane or center line. ## 13 Circular runout

Circular runout is condition that surface of revolution on part maintains a fixed position relative to reference axis within defined measurement plane. Circular runout tolerance is maximum allowable variation within limited measurement range when actual element to be measured rotates a full circle around reference axis without axial movement.
Example 1: Tolerance zone is area between two concentric circles that are perpendicular to any measurement plane, radius difference is 0.1mm, and center of circle is on same reference axis. Example 2: Tolerance zone is area between two circles with a distance of 0.1mm on measuring cylinder at any radial position coaxial with datum.

## 14 Full runout

Full runout refers to amount of runout along the entire measured surface when part rotates continuously around reference axis. Full runout tolerance is maximum amount of runout allowed when actual feature under test is continuously rotated about reference axis while indicator moves relative to its ideal contour.
Example 1: Tolerance zone is area between two cylindrical surfaces with a radius difference of 0.1mm and coaxial with datum. Example 2: Tolerance zone is area between two parallel planes with a radius difference of 0.1mm and perpendicular to reference.

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