They are used as a one way gate to ensure air flow only goes in one direction.
Metal Back Draught Shutter Damper, Spring Loaded Non Return Valve Backdraft Duct
Mekalero Compact Waist Mounted Fan with Spring Loaded Clip and 8 Hour Working Time for Walking and Sightseeing USB C Fast Charging Fan
Small Clip Fan - Portable Air Circulation Fan, Rechargeable Personal Cooling Device, Triple Velocity Airflow Control, Versatile Spring Loaded Clamp Mechanism, Portable Ventilation Accessory for Home
OSNIYAW Compact Waist Mounted Fan with Spring Loaded Clip and 8 Hour Working Time for Walking and Sightseeing USB C Fast Charging Fan
kmgfsd Compact Waist Mounted Fan with Spring Loaded Clip and 8 Hour Working Time for Walking and Sightseeing Sports Activity Fan
Spring Loaded Vent Cover for Kitchen Wall or Ceiling Ventilation Systems
