Jet JW1044 4-to-2-1/2-Inch Reducer 4-Inch to 2-1/2-Inch reducer allows you to step down from a larger size machine Connects 4-Inch line to 2-1/2-Inch dust ports Step down increases air velocity where it is needed most Reducer lets you adapt to many machines 2-1/2-by-4-Inch outer diameter