I have a Bernina 730E. I tried the bobbin weight thread and found on some of the denser designs the white shows up on top so when I do dense designs I use a shade of the same color on the bottom as I am working with on the top (red for reds, greens for greens, etc) I also adjusted my bobbin tension screw just a tad bit. The last batch of embroidery I did (for the grandkids) I used regular sewing thread in the bobbin and it seemed to work fine. The 730E bobbin is slightly thinner than regular Bernina bobbins so I don't know if the pre-wound will fit?