The coupling pins of your trailer hitch have a diameter of 38 mm when new. What should you note regarding wear?

You answered correctly. The coupling pins of your trailer hitch must maintain a minimum diameter of 36.5 mm over the entire coupling surface to ensure a secure and safe connection—this prevents excessive wear that could lead to dangerous play or disengagement. Additionally, the lower pin guide must not have excessive free play, since this could also affect the stability and safety of the trailer connection. These checks help maintain road safety when towing. The answer about allowing wear below 36.5 mm on one side is incorrect because the diameter must not fall below the minimum anywhere on the coupling surface. Always ensure both requirements are met before towing a trailer.