Many cheap and helpful inventions
Parts of interchangeable parts of a musket.
The musket was the only thing that was around for interchangeable parts.
There were many types of interchangeable parts for many inventions.
The hard labor
It took a lot of time and work to make the cotton gins work at the speed needed to get the work done. Many slaves had to work the cotton gin and pick it from he fields to work it to separated fibers.