My Husqvarna does not like "bobbin" thread, or "bottom-line" thread. I bought pre-wound bobbins and had nothing but problem. (My friend swears by pre-wound bobbins for her Brother machine.) Since I read that people loved the higher weight bobbin thread I was sure there was something wrong with my machine. But it worked well with the 40 weight thread, so decided to just wind my own bobbins and keep an adequate amount of bobbins available for use. About a month ago I was telling my dealer about needing a new bobbin case he said the bobbin case I have is preset for 40 weight thread. He did not recommend adjusting the bobbin case constantly but to get an extra one to use when changing to a different weight thread. My Janome isn't so concerned - about the thread weight, but it does preform better when the top thread matches the bobbin thread.