I came across some attachments like that recently. I initially thought "White" until I inspected further. I think they might belong to a New Home NLB or ALB, I think those are the models. There might be a "Free" that they fit.
Do you by any chance have a Featherweight? The FW bobbin will fit into the bobbin case. I don't know if it will actually work. I just know that a White bobbin will not fit in, but the FW bobbin will.
I don't have any machines to try them on (I probably should add a "yet" here, though
).
Janey - Neat people never make the exciting discoveries I do.