Brocktoon paid $8.4x for screws. He used 8 of them. These screws cost him $1.05 each. The rest are stock. He doesn't pay $0.17 per screw until all 50 are sold.
I'm not a CPA. Such stuff drives me nutso. I realize that this is only one way to look at it. Get the Government involved and you won't make any sense of it.
Never memorize something you can look up.