I used what I could to find out what bobbin one of my machines needed.
I had to go buy different plastic ones for the Singer Fashion Mate of the 1980's. It didn't like the metal ones from my Kenmore (1972), or the plastic ones of my Viking Rose, or Pfaff Expressions 3.0.
I have a new (to me) Singer 15-91 that I'm still trying to please completely. so far it likes the metal for my Kenmore's the best.