johnr:
China at present is the biggest manufacture of commodities. I beleive that you never come China before. So it is not strange for you to buy a screw in bad quality. If you come China you will see thousands of screws in defferent quality and price.
The problem is lots of customers(especial from US) they buy products in very low price, but in good quality. It is imporssible.
There are a Chinese proverb: one cent of value, one cent of cost.