I'm looking for an extra bobbin case for my 201. Does anyone know if they are all the same? I'm thinking the different sub models and early production versus a late production might have seen a few changes. Late 1920s to 1960s is a rather long period. I noticed there are one or two on fleabay at the moment, but not much detailed info. Mine is a 201K, cast iron with serial number dating it to 1950.