My machine takes Singer #15 plastic sided bobbins. I have 3 thread boxes, , they hold 64 large spools and can hold the bobbin on the same tab as the thread.
Sulky Slimline Universal Slimline Storage Box, so I have lots of colors. I bought 2 boxes of 36 prewound bobbins, the only duplicates were the black and white. Anyway...today I could not find the end of the thread, so now I'm here. I tried all the suggestions. I ended up
closely looking at several bobbins I had not started to use yet, with a magnifying glass. They all had the end of the thread in the center of the spool. I had been trying to find it on either of the sides. I went back to the problem one and used the scotch tape pressing on the center all the way around, and the miracle happened and the end showed itself. I hope this helps.