My 1949 Singer 15-30 uses solid metal bobbins. I have newer metal bobbins that look the same size, but my old girl does not like them. They aren’t solid, having holes on the flat top & bottom. My Brother, bought in 2013, uses plastic bobbins, but they have to be ones with a slight inward curve to the ‘flat’ top & bottom. Truly flat ones don’t work in this machine. I’ve never tried to interchange bobbins between the 2 machines.