Design Tips

  

  

ISO 2768 – General Geometrical Tolerances
2021-09-28

What is ISO2768?

 

ISO2768 is an internal ISO tolerance standard, which is to simplify the drawing specification and special the general mechanical tolerances on the drawings. SO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). 

 

ISO 2768 consists of the following parts, under the general title General tolerances:

— Part 1: Tolerances for linear and angular dimensions without individual tolerance indications

— Part 2: Geometrical tolerances for features without individual tolerance indications

 

International Standard ISO 2768-1 and Standard ISO2768-2 was prepared by Technical Committee ISO/TC 3, Limits and fits. ISO2768 mainly applies to the parts which are fabricated by CNC machining or other manufacturing process of material removing.

 

General Tolerance ISO2768-1  

 

ISO2768-1 is intended to simplify the drawing specification and indicate the general mechanical tolerances on the drawings in 4 tolerance classes, which include f-fine, m-medium, c-coarse, v-very coarse.

 

ISO2768  only applies for the following dimensions without individual tolerance specification:

a) linear dimensions (e.g. external sizes, internal sizes, step sizes, diameters, radii, distances, external radii and chamfer heights for broken edges);

b) angular dimensions, including angular dimensions usually not indicated, e.g. right angles (90°), unless reference to ISO 2768-2 is made, or angles of uniform polygons;

c) linear and angular dimensions produced by machining process or other manufacturing process of material removing.

It does not apply for the following dimensions:

a) linear and angular dimensions which are covered by reference to other standards on general tolerances;

b) auxiliary dimensions indicated in brackets;

c) theoretically exact dimensions indicated in rectangular frames.

Below are the tolerance tables related to the 4 tolerances classes.

Table 1-Linear Dimensions Tolerance

Permissible deviations in mm for   ranges in nominal lengths

 

 

Tolerance Class Designation (Description)

 

f (fine)

m (medium)

C (coarse)

 

V (very coarse)

 

0.5 up to 3

 

±0.05

 

±0.1

 

±0.2

 

 

over 3 up to 6

 

±0.05

 

±0.1

 

±0.3

 

±0.5

 

over 6 up to 30

 

±0.1

 

±0.2

 

±0.5

 

±1.0

 

over 30 up to 120

 

±0.15

 

±0.3

 

±0.8

 

±1.5

 

over 120 up to 400

 

±0.2

 

±0.5

 

±1.2

 

±2.5

 

over 400 up to 1000

±0.3

 

±0.8

 

±2.0

 

±4.0

 

over 1000 up to 2000

 

±0.5

 

±1.2

 

±3.0

 

±6.0

 

over 2000 up to 4000

 

 

±2.0

 

±4.0

 

±8.0

 

Table 2- External Radius and Chamfer Heights Tolerance

Permissible deviations in mm for   ranges in nominal lengths

 

 

Tolerance Class Designation (Description)

 

f (fine)

m (medium)

C (coarse)

 

V (very coarse)

 

0.5 up to 3

 

±0.2

 

±0.2

 

±0.4

 

±0.4

 

over 3 up to 6

 

±0.5

 

±0.5

 

±1.0

 

±1.0

 

over 6

 

±1.0

 

±1.0

 

±2.0

 

±2.0

 

Table 3 - Angular Dimensions Tolerance

Permissible deviations in mm for ranges   in nominal lengths

 

 

Tolerance Class Designation (Description)

 

f (fine)

m (medium)

C (coarse)

 

V (very coarse)

 

up to 10

 

±1º

 

±1º

 

±1º30′

 

±3º

 

over 10 up to 50

 

±0º30′

 

±0º30′

 

±1º

 

±2º

 

over 50 up to 120

 

±0º20′

 

±0º20′

 

±0º30′

 

±1º

 

over 120 up to 400

 

±0º10′

 

±0º10′

 

±0º15′

 

±0º30′

 

over 400

 

±0º5′

 

±0º5′

 

±0º10′

 

±0º20′

 

 

General Tolerances ISO 2768-2

ISO 2768-2 is to simplify drawing and fixes general tolerances in 3 tolerance classes (H, K, and L), this part including General Geometrical Tolerances range of flatness & straightness, cylindricity, and circularity. Below is the tolerance chart related to General Tolerances ISO2768-2.

 

GENERAL TOLERANCES FOR FORM AND POSITION (DIN ISO 2768 T2)

 

STRAIGHTNESS AND FLATNESS

 

Ranges in nominal   lengths in mm

 

 

Tolerance   class

 

H

K

L

up to 10

 

0.02

0.05

0.1

over 10 up to 30

 

0.05

0.1

0.2

over 30 up to 100

 

0.1

0.2

0.4

over 100 up to 300

 

0.2

0.4

0.8

over 300 up to 1000

 

0.3

0.6

1.2

over 1000 up to 3000

 

0.4

0.8

1.6

 

PERPENDICULARITY

 

Ranges in nominal   lengths in mm

 

 

Tolerance   class

 

H      

K

L

up to 100

 

0.2

0.4

0.6

over 100 up to 300

 

0.3

0.6

1

over 300 up to 1000

 

0.4

0.8

1.5

over 1000 up to 3000

 

0.5

0.8

2

 

 

SYMMETRY

 

Ranges in nominal   lengths in mm

 

 

Tolerance   class

 

H      

K

L

up to 100

 

0.5

0.6

0.6

over 100 up to 300

 

0.5

0.6

1

over 300 up to 1000

 

0.5

0.8

1.5

over 1000 up to 3000

 

0.5

1

2

 

 

RUN-OUT

 

Tolerance class

 

H

K

L

0.1

0.2

0.5