I have three machines and the bobbins are different for each one.
My problem with the Kenmore is that Singer bobbins come in different profiles. The wrong ones I was using were taller than the correct one. I have since saprated them and put a K in Sharpie on the correct ones.
My Pfaff bobbins have a notch that has to fit in the bobbin winder.
My Vikings have to be placed a certain side up - fortunately I only buy the green ones else I would really be in bobbin h*ll.
It would certainly be too easy if they were standardized!