Caroline,
I got my 338 first, then found the same goodie box. Made the ensemble complete. The 338 is an all metal ZZ machine that must have the ZZ cam in it to do the ZZ stitch. But with over 30 flat cams available you can do alllllllll sorts of decorative stitches.
Oh, and as with all of Singers all metal ZZ machines, it loves Tri-Flow.
Ours is in the way, but I refuse to get rid of it. Least wise not yet.
Joe