Hey, ive been wondering about my pickups for awhile now, i have pickups that look like double coils, but the one side has screws in it. Does that do anything? or does it just take up space? Because im pretty sure that screws dont pick up vibrations from the strings to give me sound, or my knowledge of physics is a bit wrong.
Taken From wikipedia... http://en.wikipedia.org/wiki/Humbucker

Quote by Wikipedia
A conventional humbucker (or Humbucking pickup) is a type of electric guitar pickup that uses two coils, both generating string signal. Humbuckers have high output since both coils are in series and because the magnetic circuit is low loss. Since the two coils are of reversed polarity and reverse-wound and connected in series, noise and interference is significantly reduced via common-mode rejection. They get their name because they cancel out a large proportion of the interference (they "buck the hum") induced by alternating current sources normally experienced with single coil pickups.

So in other words yes it does serve a purpose.
ESP LTD MH-1000 w/ EMGs
Ibanez S470DX w/ Duncan JB & 59'
Schecter C-1+
Peavey 5150 Combo
ISP Decimator
Maxon OD-808
MXR 10 band eq

-Delay Pedal, 2 Veteran 30 Speakers, Duncan Blackouts set, Reverb Pedal