I saw this on Sew-classic's web page:
"For Singer 15-91, 15-90, 15-88 or 15-125, this bobbin is not what you should get.(any machine that uses BC#125291). *Current manufacturing standards for the metal, class 15 bobbins often result in fitment issues.
Effective 12/13/2012- Sew-Classic no longer tests or alters these bobbins for fitment. We recommend the 2518-P instead of the metal class 15 bobbins for all machines."
http://shop.sew-classic.com/Bobbins-...ils-2518-A.htm
The plastic bobbins are inexpensive so consider them somewhat disposable. They will work for either the metal bobbin holder or the plastic bobbin holder. I think there are little liner things you can put in there to slow them down a bit, too.