Compare the bobbin number given in the instruction book for your Singer and the bobbin number for the bobbin you actually have in your machine. There are 2 of the clear plastic bobbins for use with Singer machines that appear to be identical but are actually two different sizes. I bought additional bobbins so I could have extra of several different colors, used one of them and stitches were awful. Put in one of the older ones and everything was great. Read the manual and it said to check the size of the bobbin and make sure you had the correct size. Replacing the new bobbins resolved my problem.