my first electronic machine, a Kenmore, used my old metal bobbins from my mechanical machine but I couldn't see when it got low so switched to plastic. I recently got a Baby Lock and found it needed certain, flat sided plastic bobbins and can't use my other plastic ones. But, the flat-sided plastic bobbins work in my Kenmore. So I think its a matter of experimentation, ask a maintenance tech or use what's recommended for your machine.