Sewing machines are a mystery to a lot of people, but this website
has a great animation that shows how a bobbin works.
There are 2 main parts that I will be talking about today
1. The Bobbin Case
2. The Shuttle Race/Shuttle Hook
The Shuttle Race is made of 2 parts. The part on the inside is stationary, and the part around the outside rotates and grabs the thread as you sew (aka. the hook).