Speedi-Products EX-PI 34 3-Inch to 4-Inch Round Plastic Increaser Speedi-Exhaust Products are made in the USA Ideal for adapting 3-Inch to 4-Inch to oval exhaust air duct systems Ideal for dryers, exhaust fans and range hoods Seal joints with approved duct mastic sealants & tapes Consult your local building codes for approved installation practices