Prewound bobbins are even and wound with perfect tension. I use the cardboard backed bobbins and remove the cardboard. They work in all my machines except my Singer Quantum which has sensor in the bobbin. You can read all about prewound bobbins at Superior Threads website. Mr. Bob knows what he is talking about and tells it like it is when it comes to thread. You can buy prewound bobbins in most all colors at Superior Threads or Bobbin Central.