It's difficult to reach the tension screw on the bobbin case, mine doesn't turn easily unless it's out of the machine. I have to unclick two springs on each side of the top ring and it comes of, then with a knack it clicks fairly easily into place. I struggled a lot before I realized how it was done. It's not like the case on a 15 or any other vertical bobbin machine which are out all the time anyway. Maybe I should set up a dedicated machine for top stitch thread, it would be reason to get another one in a table ;- )