GA letters on brass fittings may have many understandings. But I'll tell you one of the most common and simple explanations: GA may be the abbreviation or trademark of the manufacturer. Because each company and production line has its own unique production mode and product identification, we need to know the relevant information behind the corresponding products before dealing with specific problems.
For the 1/2 marked on the other side, it means that this pipe fitting is a pipe fitting with internal threads, and 1/2 means that the size of this solid column is 1/2 inches, which is usually used to connect pipes such as water pipes and gas pipes. Of course, if you need more professional information and technical guidance, you can consult the manufacturer or related equipment maintenance personnel.
In short, for some relatively unpopular or niche knowledge fields, it is sometimes necessary to proceed from reality and enhance the interest and initiative of learning. I hope my answer can help you and get enlightenment and help in your exploration!