The model 75B is an out of stream fire damper. It is approved for use in walls, floors, and partitions with fire resistance ratings less than 2 hours. This model carries a 1-1/2 hour UL fire damper label.
UL 555 Fire Resistance Rating. Fire resistance rated 1-1/2 Hours. Partitions materials rated 2 Hours or less.
See the documentation tab for full details.