Coil Thread End
These coil thread ends are one of the products we have sold since we opened, 18 years ago!
These ones are silver plated, and are 11x4mm with a hole for 2mm thread. The end loop can be opened to attach your clasp.
The trick is to just push that final twist of the coil into the thread, using a flat nose plier, and if your thread is a bit thin, then double or even triple it into the hole. This thread end needs a good bit of thread to be able to hold on to it, I often use a dab of glue to be really sure too.