Which device should be engaged when performing work on the counterweights?

Engaging the swing lock is essential when performing work on the counterweights because it ensures that the counterweights remain securely in place while maintenance or adjustments are being made. The swing lock is specifically designed to immobilize the counterweights, preventing them from shifting unexpectedly, which could lead to accidents or injury during work.

Counterweights are critical components in various machinery, such as cranes and lifts, providing balance and stability. When working on these parts, it's crucial to minimize risks. By using the swing lock, operators can safely manage the counterweights, ensuring that they do not swing or drop during the operation.

Other types of locks, like the safety lock, emergency lock, and weight lock, serve different purposes related to safety and equipment functionality, but they do not specifically address the need for immobilizing the counterweights during maintenance. Therefore, the swing lock is the correct choice for this particular task.