Which feature in tower operations allows for ensuring that signals can be sent and received safely?

The lever stop parts play a crucial role in tower operations by preventing levers from being moved into positions that could create conflicting signal indications. These parts ensure that a signal cannot be set or changed when the current conditions would lead to unsafe operations, such as allowing a train to proceed onto a track that is already occupied. By doing this, lever stop parts help maintain the safety of train movements by ensuring that signals are aligned correctly with the physical state of the track and other operational components. This safety mechanism is important in preventing accidents and ensuring the efficiency of train operations, making this feature essential for safe signal communication in tower operations.