I'm guessing you do not have the manual for it. It looks like it would fit a vintage White. I have vintage Greist Decorative Zigzagger attachment that is Style #1 which is for a low shank machine. The manual has three types (Styles). The #2 is for round bars, but the knob needs to be removed to attach the attachment.
This is the page from the buttonhole attachment for a White machines that have the top clamp, like the 11, 43, 77 and FR.
I think that it might work with any of the top clamp machines as shown at
http://ismacs.net/needle_and_shank/shank.html
Janey - Neat people never make the exciting discoveries I do.
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