Fan & Fixture Mounting Box with Adjustable Brackets for New Construction. Mounts fans and fixtures on cathedral ceilings between two framing members for perfect centering within room. Expandable brackets hold box securely between joists – no need to cut and nail 2x4s to center the fan or fixture. Allows fans/fixtures to be perfectly centered within room. Large, 8” square mounting surface handles newer fans with larger canopies. No loose parts to misplace – totally self-contained! Installs quickly and securely.