happyquiltmom,
I have bobbins made from the early 1900s that were machined from on piece on a lathe and used in the Singer 9W-7 machines, that work in my FW. I've got original FW bobbins too. We've also got some that did come from eBay years ago and they work.
There is many many variations possible due to tolerance variations.
And then .... here is a reason many things made overseas do not
fit American made products properly.
A little story to illustrate my point.
http://en.wikipedia.org/wiki/Tupolev_Tu-4
That is part of the problem of using foreign made parts in American made sewing machines. Sometimes the manufacturers do not make them to inch specifications, but they round them to the nearest millimeter. So because of that, a lot of times they are too big.
Joe