My 1956 201 and both 1927 Redeye treadles cannot use the modern 66 class metal bobbins. Strangely enough the plastic 66s work just fine. Sew-Classic gave me that tip and assured me their metal bobbins would fit when she gets them in stock again. Anyway, the new bobbin's diameter is too wide and won't even drop into the case. The two vintage bobbins I have work perfectly. Now if only I could find a source for vintage bobbins.