According to
https://tumorfarmer.blogspot.com/202...chine-cam.html the cams that came with the 158.481 are shown at
https://blogger.googleusercontent.co...g+machines.JPG I don't see any that have metal on them.
I am unable to find out for sure if your wife's machine would be a high or low shank machine. I'm guessing the manual has gone missing as well as the "tool." Looking at the above blogspot, there is an advertisement and is possibly for your wife's machine. It mentions a built-in buttonholer. If you could post a picture or more (can only attach 5 per post directions given above) it would help tremendously.
As mentioned before, I prefer the attachment. I have a few machines with built-in buttonholers. My main machine for many years had a dial to turn to make buttonholes. I ended up getting a couple of buttonhole attachments to make buttonholes, as I didn't like the built-in kind. There were lots of buttonhole attachments over the years to fit many different machines. If one does get the buttonhole attachment, you need to make sure it will fit the machine. Even though many look the same they are not all the same. Again a picture of the machine's needle area would help determine which buttonhole attachment would work.