Reducing cross: A cross-shaped structure, usually the main pipe (two opposite ports) has the same diameter, and the branch pipe (the other two opposite ports) has the same diameter but different from the main pipe (or the four ports have different diameters). Used for cross-diversion/confluence with variable diameters.

Note on reducing crosses: When using reducing crosses, you also need to pay attention to stress concentration and flow velocity changes at the point where the diameter changes.