Derale Standard Rotation Rigid Steel 6 Blade Race Fan Black 17-3/4 Inch Rated to 8,000 Rpm Blade Pitch 28⁰ 17518. Features:- Aluminium fan blades. Maximum full time airflow. Rated up to 8,000 RPM. 17-3/4″ standard rotation rigid fan design. Specifications:- Flange bolt spacing: 1-3/4″ – 2-1/4″. Depth: 2 1/4″. Mounting surface to front: 1 7/16″. Mounting surface to rear: 3/4″. Rotation: Standard (clockwise). Construction: Powder coated black steel hub.