Welcome to the new version of the Patents Manual. Please note there are changes to the numbering and sequence of the chapters and pages in the manual. You are encouraged to take the time to explore and familiarise yourself with this new structure. Combination Set (C-set)

Date Published

C-set classification is a special classification technique, providing a mechanism for searching combined features that are otherwise not easy to find by single symbols, resulting in more precise and efficient retrieval of technical information from the CPC.


C-sets are a combination of CPC symbols used for classifying combined technical features that cannot be adequately covered by the allocation of a single symbol.


  • The C-Set (A, B) may denote a specific mixture of chemical compounds A and B.
  • The C-Set (A, B) can also denote a chemical compound A and its specific process of making B.

C-Sets can also define the relationship of related technical features.

  • Example: The C-Set (S1, S2, S3), displaying a specific order of symbols, may denote a specific order or sequence of operations S1, S2, S3 in a multi-step process.

A C-Set can also define:

  • a chemical compound and the specific process of making it
  • the technical features or materials of a particular method
  • a specific mixture of chemical compounds
  • the components of a formulation
  • the function of an ingredient
  • the different steps of a multistep process


A C-Set:

  • comprises a group of at least two ranked valid CPC symbols (main-trunk classification symbols or indexing codes), separated by commas
  • brings together symbols from different groups within the same subclass or from different subclasses, in a certain order.








rank 1

rank 2

rank 3

  • C05C9/005: The first symbol is designated as the “base symbol”, and has the Rank 1 in the database.
  • C05D9/02: The second symbol is designated as the “subsequent symbol”, and has the Rank 2 in the database.
  • C05G3/0058: Any further symbol, if present, is also designated as “subsequent symbol”, and has the Rank 3 or higher in the database.


To ensure classification accuracy and consistency, C-Sets classification is authorised only in a limited number of CPC subclasses. The table in Annex III of the CPC guide lists those subclasses authorised for C-Sets allocation. As shown in the Table, not all groups within the authorized subclasses are allowed for C-Sets allocation.

A list of all areas of the CPC that allows the use of C-Sets can be found on the CPC website.

This list is updated if new areas are authorised to use C-Sets.

Amended Reasons

Amended Reason Date Amended

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