They are used to direct the magnetic field from its magnetic path within the pickup towards the strings. Some pole pieces are rod or bar alnico or ceramic magnets and others are ferrous poles (studs) or ferrous bars that act as pole pieces to magnetize the strings. The further away the pickup is from the strings the less magnetic flux for the strings to move back and forth through the coil.

Some pole pieces are staggered as in Vintage style Stratocaster pickups; this was done to balance the output of each string being used at the time. Modern strings are pretty equal today and many pickups use flush or the same height poles from E to E. One problem with poles that are equal or the same height is that they do not compensate for the radius in the bridge and strings. The two outer lower strings (E & E) can be louder than the two inner strings (D & G).

Having the poles staggered in the traditional way is very important to the total sound a vintage Stratocaster pickup will sound. Each magnetic rod pole piece with different lengths will have different magnetic effects within the coil.