The surface of the lock is corroded much more poorly than the shaft. Such phenomenon also occurs in many other locks in the school.

The rusting should be stopped, or when the inside of the lock is corroded, roughness makes opening the door difficult. Damages to the lock is possible.

Zinc-plating has been used to prevent rusting. Adding oil for lubrication is important to make the surface inside smooth. Replacing old locks with locks made with corrosion-resisting alloy is suggested if possible.