There are many surface treatments during the manufacturing of a machine part. Providing precise relation of all surfaces with each other increases the cost too much, therefore the processing cost is reduced by precise treatment of the relations between only the most necessary surfaces.

Only surface treatment markings and dimensional tolerances may not be sufficient to ensure that the machine parts are treated at the precision specified above. Example: Ensuring that a surface of a machine part is parallel or perpendicular to another surface of the same part within a certain tolerance, or ensuring that the ovalness of a bore or that it is aligned with another bore in the same axis can not be achieved only with dimensional tolerance and surface treatment marks.  In these cases boundry tolerances should be used.

Boundry tolerances are indicated by symbols in side-by-side boxes.

• In the first box is the symbol of surface relations such as linearity, parallelism, and perpendicularity.
• The diameter symbol is indicated in the second box if the surface tolerance to be treated is within a cylindrical area. If it's a flat surface, this symbol is not used.
• In the third box, the precision measurement is indicated in millimeters.
• In the fourth box, it is indicated to which method the material will be treated in order to reach the specified precision. See Table 5. If the method has no significance, this symbol is not used.
• In the fifth box and the ones on its right, there are the letters indicating the reference surfaces.  These surfaces may be more than one (such as A, B, C)

Geometric Shape and Tolerance Indications are standardized with DIN ISO1101 norm. The main ones of these standards are provided in the following tables. These are;

The degree of roughness in the DIN 3142 norm used in Turkey is indicated by the Ra value.

From time to time, we can come across surface treatment value in ASA 46-1 norm for the projects from US or Canada.  The values in the ASA norm are 40 times the values in the DIN3142 norm.