The main idea of this excerpt is that factory work was dangerous and not easy, even though we do not know much about the context; it is quite simple to understand the main point of the excerpt.
the final final sentence gives all the key details that we need to understand the main idea of this excerpt. By stating that: Fingers, hair, and clothing often got caught in the gears and belts of machines. We can easily understand why it is said that factory work is dangerous, you can lose fingers, be drawn into machinery and get really hurt or even killed.
So the final answer to this questions is:
Fingers, hair, and clothing often got caught in the gears and belts of machines
