This internal hardware component provides the tension necessary for a door knob or lever to snap back to horizontal once released. It operates in tandem with the latch bolt spring to ensure the door remains securely latched. When a door handle sags or fails to retract the latch properly, a broken or fatigued spring is usually the culprit.
Heard on the job
The lever is drooping on the bathroom door because the return spring inside the rose has snapped.