Roof Ventilator Base Adapter, Function Adapts 27-3/4 in Round Base to 28 in Square Base, Material Steel, Overall Width 28 in, For Round Base Diameter 27 3/4 in, Flange Height 1 3/4 in, Compatible Grainger Part Number 4HZ58, 4ZH59, 5DVN1, 5DVN2, 5DVR1, Finish Galvanized, For Fan Type Upblast Fans, Includes (6) Bolts, (6) Nuts, Metal Material Thickness 1.7 in