What is the maximum vertical play permitted for a coupling pin?

You answered correctly. For coupling pins, the maximum allowed vertical play is 4 mm. This rule exists to ensure a secure connection between vehicles, such as trucks and trailers. Excessive play can lead to unsafe driving conditions or even accidental decoupling. If the vertical play is more than 4 mm, the coupling is considered worn and must be repaired or replaced for safety. Always check that the vertical play does not exceed the allowed limit before starting your journey. This is part of the standard safety inspection for vehicles with towing equipment in Germany.