2-1/2″ Flexible duct hose adapter with a square mounting flange. The adapter is made of injection molded abs plastic, and features a square flange that will mount to any flat surface. The flange measures 3-1/2″ x 3-1/2″, and the adapter is 1-1/4″ tall. The flange has four holes in each corner for 1/8″ screws.