This gauge allows embroiderers to consistently set accurate embroidery bobbin case tension on style M jumbo embroidery bobbin cases. With the Towa Bobbin Case Tension Gauge the guesswork is gone forever. In just a few seconds you can verify your bobbin tension is where it should be to achieve optimum results. It's simple to use and comes with complete instructions. No setup is required. It's ready to use right out of the box.