A bobbin's dimensions (height and diameter) is called its style or type. Each sewing machine is designed to work with a specific bobbin style. So, the first step in bobbin-buying is to determine your machine's style. Style A bobbins are sometimes called universal bobbins. They are used with home and small commercial machines for sewing and embroidery. Style A bobbins are 0.465 inches (1.181 cm) high and 0.815 inches (2.070 cm) in diameter. They are thicker than Style L bobbins.
Check your machine's manual or your dealer to find out which style bobbin your machine requires.