4" to 2" allows you to reduce from a 4" hose down to a 2" hose. Hose clamps are required for proper fitting. Many sizes of Reducers / Splices available. Each sold separately. They are 5" to 4", 4" to 3", 4" to 2 1/2", 3" to 2 1/2", 3" to 2", 1 1/2" to 2 1/2", 4" to 1", 2 1/2" hard splice, 2 1/2" screw adapter end, 2 1/2" hose splice, 4" hose splice