This adaptor allows you to combine two hoses with different diameters (12/16 mm to 16/22 mm), especially in a fish tank. This is useful if your filter has a different water-output than your aquarium inflow. The outer diameter of the adaptor is a millimeter bigger than the actual inner diameter of the hose in order to keep it tight in place. Therefore, it might be helpful to heat the hoses in hot water before pushing it over the adaptor. This makes the hoses more flexible and easier to push over the adaptor. The adaptor itself should not be heated, because it could deform, and leaks may occur.
Of, course this adaptor may not only be used for a tank. If the material properties are fine, there might be various use cases.
The author marked this model as their own original creation.