What is the role of a bobbin in machine stitching?

• A. It provides the lower thread that forms the lock with the upper thread.
• B. It holds the upper thread.
• C. It trims the thread.
• D. It guides fabric.

Answer: (A)

The bobbin provides the lower thread that forms the lock with the upper thread. In a sewing machine, the needle carries the upper thread and the bobbin sits in its case under the needle plate, supplying the thread from below. As the machine sews, the hook catches the upper thread and loops it around the bobbin thread, creating a balanced lockstitch visible on both sides of the fabric. This interaction between the two threads is what holds stitches securely.

The bobbin isn’t responsible for holding the upper thread—that’s the job of the needle system and take-up mechanism. It doesn’t trim thread either; trimming is done by a cutter or blade. And it doesn’t guide fabric—that’s the role of the presser foot and feed dogs.