I have no clue.... I have a question tho.... I have used ( dont know what size) prewound bobbines in my Brother SE- 350 with out problems... MY problem arrives when I try to get the bobbin started.. how do u find the starting thread??? or is it just the bobbins I happened to purchase that as that difficult to fint the end thread???? I know I have visual problems, but even DH tried even under maginfication.....