Standard construction Frame: 20ga. galvanized steel. Blade: Single blade 20ga. galvanized steel Axle: 3/8" dia. galvanized steel bolted to blade Max. section size: 18" dia. Min. section size: 4" dia. Hand Quadrant: for manual operation Installation instruction Air flow rate control Between Duct and Duct bolt connection Variations 1. Special finishes 2. special materials 3. Special thickness of blade or frame Note 1/8" deducted "D" unless otherwise specified.