Please, when you design a product, write a manual which gives you a bag of screws and then asks you to pick the M-1-8-15mm screw. Good god, what on earth is the 1-8 and what does the 15mm stand for? As an engineer I did not actually find this confusing. But please, I suspect we are not all engineers.
A better solution? Manufacture the screws with a drop of colored paint on the head, and make the manual read "Put the screw with the red top in the red hole, put the screw with the green top in the green hole." Is that really that hard to do?
If you can't paint the top, how about describing things like this:
This product is manufactured with three different sized screws. Please open the bag and divide them into small, medium, and large. Now... take one small screw and put it in the hole labeled 'S' ." Can't we just do that?