They are a different size than my 7570 bobbins. 7570 bobbins are smaller around and shorter, they are sloppy in the 939 case. A real bummer as I have a lot of bobbins for the 7570. Am too chicken to even try a 7570 in the 939 to see if it might work.
I have sent the company an email to make sure I order the right size for the 939. Amazon has the same #9033P and some people say they do not fit their newer machines.