Ideal for woodworkers with Shop-Vacs or the equivalent, the Jet 4-Inch to 2-1/2-Inch Reducer allows you to step down from a larger size machine. The reducer connects 4-inch line to 2-1/2-inch dust ports. The step down increases air velocity where it is needed most. With an outer diameter of 2-1/2-by-4-inches, this reducer lets you adapt to many machines.