what are the fuction of the pick-ups top screws?

[Otto Orraca]

I thank you for that information I have a better understanding of them. as Strings goes, what strings would you recomend, I had a set of DR lowriders with a .125 B string that I try on it but I didn't like them they sounded like a can metal, I hear that "clank" sound. I don't like the strings to be too bright.