• The GT code is made up of a string of digits which identify specific attributes of a part.


• If the digits of a GT code are unrelated, it is a polycode, and each digit may be looked up independently.


• If the digits of a GT code are related, it is a monocode, and they must be looked up in sequence.


• It is possible to have a hybrid GT code which is a combination of polycode and monocode.


• When selecting what the GT digits represent, the guidelines are,

• They must differentiate products

• Must represent non-trivial features

• Only critical features should be encoded

• Function should be encoded

• Every digit should be significant





• Parts can be encoded using

- process flow

- tool axis

- tolerance

- function

- material

- shape.



3.2.1 Optiz Code


• One example system is the popular Opitz code, developed in a German university by H.Opitz.


• This code uses a sequence of 5 digits, 4 digits, and 4 letters, such as ‘11223 4455 ADEA’

- The first five digits are the form code (identify shape). See the table for form codes.

- The next four digits are the supplementary code - used to represent non-form details such as tolerances, materials, etc.

- The last four letters are the secondary code, used to represent production operation types, sequences, or other functions chosen by the manufacturer.


• The Opitz code for a part is constructed from the first digit on, as shown in the tables below.




3.2.2 Decision Tree


• Decision trees are developed to be specific to typical product line, or manufacturing facility.


• To develop one of these trees we draw a tree that shows alternate possibilities for a part, and then number the options (care must be used to leave options not anticipated).


• Part of an example decision tree is given below. This can be expanded as it applies to a particular manufacturer or industry.