If you've wondered about the parts that go into a Humbucker. Here's the parts list.
Parts laid out before assembly. Raw Nickel cover, Nickel/Silver baseplate.
Butyrate Bobbin. Wire is wrapped around it to create the coil. The original Gibson PAF called for 5,000 turns per coil, half of what it's predecessor the P90 called for. The original winding machines lacked an automatic stop, so the turns count could vary as the machine operator let them run over or under.
Alnico bar magnets. These are graded by magnetic strength, A2, A3, A4 ,A5, A8 all sound different. The one pictured above is A4, a personal favourite.
The metal keeper supports the screw side bobbin. The 6 Screw poles pass through to the baseplate. The type of steel used affects the sound of the pickup.
The spacer supports the slug side bobbin. The one above is a maple spacer. Some pickups use a plastic spacer, but the original design called for maple. Maple will compress just slightly when assembling the pickup, keeping things snug, helps preventing microphonic feedback when making an unpotted pickup.
Here's the spacer, magnet and keeper laid out on the baseplate. You can see how the pole screws pass through the keeper. The space beside the magnet on the right is for the slugs and the maple spacer supports the bobbin. Notice on the far left there is a space for the braided shield conductor.
Pole Pieces. Nickel plated steel. The carbon content of the steel affects the tone of the pickup. The screws are 5-40 Fillister head screws. The original Seth Lover design called for two slug pole bobbins, but the execs thought having an adjustable pole piece was a good marketing feature, so they went with exposed screws on one side of the pickup.
Brass screw attach the bobbins to the baseplate from the underside of the baseplate. The screws are in the magnetic field of the pickup, so the metallurgy can affect the tone.
For comparison, here is a regular ABS plastic bobbin on the left and a Butyrate bobbin on the right.