I bought a heater from Car Builder, along with ducts for window heat. The problem - the heater outlets were 54mm and the duct inlets were 50mm. After looking at a few things to make this work, I spotted these ducting flanges. They are perfect for adjusting the outlet of the heater. You should put them together on the same page so untalented mechanics like me see them quickly! Great part and now a great working system!