Custodian Engineer Book Practice Test

The set screw plays a critical role in securing the doorknob to its spindle, ensuring that it does not rotate freely. By tightening the set screw against the spindle, it creates a friction lock that holds the doorknob in place. This prevents the doorknob from moving independently from the spindle, which is essential for the proper functioning of the locking mechanism and the overall security of the door.

In contrast, a lock mechanism is primarily responsible for engaging or disengaging the lock itself, affecting the door's ability to be opened or closed but not directly stabilizing the doorknob's position. A deadbolt is a type of lock that provides an additional level of security but also does not influence the doorknob's rotation on the spindle. A spring latch, while it assists in keeping the door closed and may engage with the strike plate, does not provide stability to the doorknob's movement either. Therefore, the function of preventing the doorknob from rotating singularly resides with the set screw.