Towa Bobbin Case Tension Gauge M
Specifically for the M size bobbin cases. This amazing tool gage will relieve the stress of not knowing if your bobbin case tension is set correctly. Just set your tension for between 190 and 220, aiming for closer to 200. This will help you to know that the only tension you need to adjust is the top tension.
This is for Size "M" bobbins only.