Welcome. I'm not much help as bkay said it is hard to find manuals for
some most of these vintage machines. Are there any JA or JC numbers on the base? Not a great pictures but has JC 27 and JA 13 that can be seen at
http://www.doubleveil.net/zssmp/resources.htm#jajc . Also
http://www.doubleveil.net/zssmp/resources.htm#jajc has some pictures and tells a bit about them. It is kind of a pain to go through but there
are were threading diagrams on a website. Fortunately, you can still get to them at
http://web.archive.org/web/201604021...g_Diagrams.htm I don't know if this one might help
https://web.archive.org/web/20160428...ng_Diagram.htm