Class 42 of trademark registration refers to the trademark classification related to scientific and technical services. The following are several common subcategories in Category 42:

1. Scientific and technological research services: including scientific research, industrial research, medical research, agricultural research, etc.

2. Industrial analysis and research services: including services for analysis and research of industrial processes, products and materials.

3. Services for designing and developing computer hardware and software: including the design, development, customization and maintenance of computer hardware and software.

4. Scientific and technological information provision services: including the provision of scientific and technological information, technical consulting, technical investigation and technical assessment services.

5. Technology project management services: including services for management, supervision and coordination of technology projects.

6. Technical consulting and research: including providing consulting and research services on technical and engineering issues.

Please note that the above are only some common subclasses within Class 42, and the actual trademark classification may be more detailed and specific. In a trademark registration application, depending on your specific business and service content, you need to select an appropriate subcategory to ensure accurate classification of the trademark.

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