If I remember correctly. Bernina uses Mettler metrosene thread (this is a poly) to calibrate their machines with when they come from the factory. Most machine manufacturers pick a thread to use as the standard when adjusting their machines. However, most machines will do well with most quality threads. I use mostly Aurfil 50 weight cotton, and Mettler so soft 50 weight cotton threads in my Bernina and don't have problems with those threads. I also have used the old standby dual duty coats and clark when have the color I want as I used to use that thread years ago. I have also used some Superior so fine poly thread with no problems. I say, try them Years ago, I used "Star" thread and I did have problems with that one breaking. Also, use a needle recommended for the size and type of thread you are using.