At the beginning years of the 216 engine (1937-1938) the fan blade that cooled the radiator was made with a center hub plus four blades. Each blade was attached to the hub with three rivets.
This combination worked well when new, however, it was certainly more expensive to produce. A dangerous part of the design was the blades attached by rivets. Rain water while driving and sometimes a leaking radiator allowed dampness to get between the blades where they overlapped the center hub. As rust continued, the chance of a blade coming loose increased. Even with deterioration, the four blades stayed in balance while the vehicle was moving. Then all #*!# broke loose when a blade went through the hood, radiator, or where-ever!
A new design fan was introduced in 1939 and used through all the remaining 216 years and early 235 year, 1954. This blade was used on Chevrolet cars and pickup trucks. It is simply two identical blades welded together that held tight against the water pump with four fasteners. Much less expensive to produce and so much safer!!!
Close-Up of 1937-1938 Fan Blade with Rivets.
1937-1938 Fan Blade with rivets.
Close-Up of the new improved safer 1939-1954 Fan Blade
1939-1954 Fan Blade