You will want metal class 66 bobbins. I would
not get the ones like
https://www.amazon.com/SINGER-2139-C...002G3YNBG?th=1 as they do not have a smooth top.
It looks like the following should be okay.
https://singer-featherweight.com/pro...inger-66-class
https://www.amazon.com/Bobbin-17222-.../dp/B0040ZFPBK
https://www.amazon.com/bobbins-Sewin...14&sr=8-5&th=1
Janey - Neat people never make the exciting discoveries I do.
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