SMSFL units are long male-to-female couplings for connecting ventilation fittings. They can be used for connecting fittings to spiral ducts without a press-in stop. If there is no press-in stop in the ducts, the end's insertion length can be freely adjusted. It is a popular solution for ventilation ducts continuously exposed to temperature variations which affect thermal expansion and shrinking of the ductwork. The fitting is also perfect for connecting fire dampers to the ductwork.
