About this 3D model

50mm inner diameter to 25mm inner diameter exhaust pipe connector. Used to connect an exhaust pipe with an inner diameter of 25mm (left image below) and an exhaust pipe with an inner diameter of 50mm (right image below). Why is the design so strange? Because I bought the 50mm inner diameter exhaust pipe and 50mm pipe fan first, and I need to open the window to exhaust air. This won't do. It exhausts but not completely. So, I had a sudden idea, I went through the hole in the outer wall of the air conditioner pipe. So I bought a 25mm air pipe, which can pass through, perfect.