This fits the Towa Brand M Size Bobbin Cases. Has two little metal spring arms that ride against the bobbin side.
What brand is my bobbin case?
There are two different types of backlash springs available for the bobbin case. It is very important when ordering and replacing the backlash spring to use the correct part. Placing the wrong backlash spring in your bobbin case will result in extreme tension problems. Because the spring designs are different, only the proper spring will fit in the proper case.
The Towa bobbin case must have the Towa or beehive backlash spring installed. You can easily identify the Towa bobbin case by the "Y" inside the circle located on the side of the bobbin case.