This is an original 1937-55 Chevy Truck Extra Cooling 6 Blade 18" Fan.  Pretty decent condition, solid, few dings/small dents and some lite pitting in areas-see photos.  Few blades may need some minor straightening-see photos.  The diameter of the center hole is approx 1".  Center to center of the mounting bolt holes is approx 1 5/8" next to each other and approx 2 1/4" diagonally.  GM Book shows this fits '37-55 Chevy Utility Trucks (also shows note about fitment on '37-38 trucks)-see last photos for pages in GM books for reference.  Will also fit smaller pickups if you wanted extra cooling.  Correct for trucks with a 216 or 235 - 6 cylinder engine-Not for 261.  May also fit cars, but would need to make sure there is enough room for an 18" diameter fan.  Please check my other auctions.