The labor for this many nails is intense. They had to first smelt the iron, cast the pigs, "puddle" the cast iron to remove carbon and make wrought iron, hammer the wrought into rod, and THEN they could start making the nails.
800,000 nails × 3 minutes = 2.4 million minutes
= 40,000 hours
= 20 Years of labor
800,000 nails × 3 minutes = 2.4 million minutes = 40,000 hours = 20 Years of labor