8" x 8" x 8" Duct Wye Branch HVAC Ductwork AC Duct Fittings High Quality Sheet Metal Air Duct Fitting. Dimensions 2 and 3 are crimped. SMK has made AC Repair and ventilation modification easy. Wye Branches are the correct way to split your vent duct. Easily add a new branch onto your ductwork, but don't forget the damper! Works with both flexible and rigid air conditioning duct.