Singer 403 A bobbin
I have my late mother's 403 A with all the attachments and cams, and looked forward to using it at our home-away-from-home in the mountains. It has only one bobbin and no manual. An online search indicated that it uses Class 66 bobbins. I bought a pack of 4 metal Class 66 bobbins, and though they look identical to the old one, the center hole is too small to fit on the bobbin winder. Is it just a fluke? Have they changed the specs on Class 66 since 1960? I'd appreciate any help.