The flange is used for positioning.

For example, the cylinder has a mounting method called flange mounting. For example, a rectangular hole is placed around a rectangular parallelepiped. A large hole is in the middle and the outer diameter of the cylinder is the same. The rectangular parallelepiped is placed on the cylinder and the other can be welded. The way is fixed together, the connection between the cylinder and other things is connected by the four holes around the cuboid. This cuboid can be called blue.