John E. has responded to Tabitha. Here is the information he gave her:
According to a 1910 catalog on CS Bell Company, a #3 1/2 is a Farm Bell 21" in diameter, 100 lbs., Costing $12. in 1910 (about three weeks wages).
CS Bell Co. made five sizes of Farm Bells:
#1 15" 40 lbs 1910 price $4.
#2 17" 50 lbs 1910 price $5.
#3 19" 75 lbs. 1910 price $7.50
#3 1/2" 21" 100 lbs. 1910 price $12.
#4 21" 100 lbs. 1910 price $10.
Note that the diameter listed is the diameter of the mold; iron shrinks upon casting, so the final actual diameter would be smaller that the mold.
CS Bell Co. marketed through Sears Roebuck & Co. and was the most prolific cast iron bell foundry. The foundry stopped producing bells for WWII, around 1939, and officially closed 1950. Your bell is at least 70 years old.
I have been buying & selling bells for 20 years; Farm Bell #1 & #2 are very common, however in 20 years I have never seen a #3 1/2 bell .... you have a rare bell.