When the bobbin thread breaks, check the following possible causes and solutions.

• The bobbin thread was not set correctly.
  
  Reset the bobbin thread correctly.
  For details on setting the bobbin thread, refer to "How do I set the bobbin?".
  
  
   
• Bobbin thread is incorrectly wound.
  
  Rewind the bobbin thread correctly.
  For details on  winding the bobbin, refer to "How do I wind the bobbin?".
  
  
   
• There are scratches on the bobbin.
  
  Replace the bobbin with a new one.
  
  
   
• The thread is tangled.
  
  Remove the tangled thread and clean the race.
  
  
   
• A bobbin designed specifically for this machine is not used.
  
  Incorrect bobbins will not work properly.
  Be sure to use the plastic bobbin that comes with the machine or bobbins of the same type.
  The bobbin's height is 11.5 mm (approx. 7/16 inch). SA156 is a Class 15 type bobbin.

  (1) 11.5 mm (approx. 7/16 inch)