What is the critical safety inspection check regarding the Fifth Wheel (Plato de Enganche / Quinta Rueda) and Kingpin (Perno Rey) when coupling a tractor to a semitrailer?

1. Ensure the fifth wheel plate is painted bright yellow
2. Visually confirm that the fifth wheel locking jaws have fully closed around the kingpin shank and the manual safety release handle is in the locked position
3. Verify that the kingpin is lubricated with water instead of grease
4. Ensure that there is a 5 cm gap between the fifth wheel and trailer apron plate