This is funny, I thought at first this was something to put your bobbins in to wash them! I was thinking, oh, that is a good idea!!! LOL

I use them in all my machines that have a metal bobbin case. It prevents static electricity and backlash when starting a seam. I've had the same package for over 3 years. They never see to wear out but I tend to drop one and never able to find it.