Pickups are usually made with a pole piece for each string. Some pickups can use blades, steel rods, magnet rods, bar magnets, double poles per string and multiple poles per string. At times you will see pickups with solid covers, and underneath their can be one coil or two in humbucking style and looking pickups. The bobbins under the cover may have a pole for each string or some may use a bar to cover all the strings. Using different types of bobbins and pole arrangements will give you different types of tone and output from a pickup.