What is the purpose of a case-hardened screw in door locks?

A case-hardened screw is specifically designed to improve security, making option B the correct choice. These screws undergo a specialized heat treatment process that hardens their outer layer while keeping their inner core tough and resilient. This combination creates a robust surface that is resistant to wear, tearing, and tampering, which is essential in securing door locks.

By using case-hardened screws in door locks, the assembly becomes much more difficult to compromise through brute force attacks such as drilling, snapping, or shearing. Therefore, their primary function is to bolster the overall security of a locking mechanism, ensuring that the lock performs effectively under potential stress or attempted forced entry.

The other options do not correctly describe the main function of case-hardened screws. They are not designed to provide aesthetic appeal, reduce weight, or simplify installation, which further underscores the importance of their role in enhancing security against physical intrusion.