A bobbin is a reel-like shape that holds the bottom thread for machine stitching. Bobbins can be made of metal or plastic. The thread is wound tightly from the center out. You can wind bobbins on your sewing machine or on a bobbin winding machine. Pre-wound bobbins are also available for purchase from thread manufacturers.
It would be great if there was a universal bobbin but unfortunately each sewing machine works with a specific bobbin size.
The thread from the bobbin will appear on the back of your quilt. It may or may not match the thread on the top of the quilt (quilter’s choice).