@bdade073 Constructive Solid Geometry. Imagine all you have is squares and circles. You can make boxes or spheres or cones. You can add a shape, wrap two shapes in a solid sheet, and you can take a shape out like a slice out of a cake. Repeat that until you have the final shape you want. That's the sort of modelling a practical print like a plumbing part probably needs to be made with. My aircon service guy also 3D models and prints his own components.