Bobbin
Definition
A bobbin is the spool of thread under the needle plate of a sewing machine that supplies the lower thread, which interlocks with the upper thread to form each stitch.
A lockstitch machine makes every stitch from two threads: the upper thread, carried by the needle, and the bobbin thread, held below. A rotating hook catches the upper thread and loops it around the bobbin thread, locking them together inside the fabric.
There are two common setups:
- Drop-in (top-loading) bobbins sit flat under a clear cover in the needle plate, so you can see how much thread is left.
- Front-loading bobbins go into a removable metal bobbin case, inserted behind a door at the front or side of the machine.
Bobbins look alike but are not interchangeable. Types such as class 15, class 66 and L-style differ by fractions of a millimeter, and the wrong one causes skipped stitches and jams. Use the type your manual specifies.
Wind bobbins on the machine's winder, evenly and not too fast, and use the same thread as on top for most sewing. A bobbin wound unevenly, or inserted the wrong way round, is behind many thread tension problems.
Bobbin thread also has special uses: when you gather fabric, you pull the bobbin threads, and shirring is sewn with elastic thread wound by hand onto the bobbin. Threading and winding are covered in sewing machine basics.