Oh, Mr. Greist, where have you been my entire sewing life? Though branded to go with my vintage Viking 6020 machine, this is really just a Greist buttonhole attachment I found on e-Bay for $15 – best sewing money I have ever spent! It makes absolutely and perfectly consistent buttonholes with one of 13 cams. And you can adjust bead size and gap spread to your heart’s content – an amazing piece of antique sewing technology!!!