Originally Posted by
elliot
The 328K is a zig zag machine that can also do other specialty stitches with disks. A 15-91 and 99 are straight stitch only machines. I believe the 328K may be a slant needle also whereas the other two are low shank and straight.
HTH
I have had a Singer 328K since 1963 or 1964, bought it new. It is not a slant needle, I have everything it originally came with. I don't know if the feet or fashion disks can be used on any other machines. All my other machines are newer and don't take anything like those, I only use what came with them.