I saw these used at the long arm demo this weekend for threading long arm quilt machines. I would think they would be too short to fit through a serger tube, but maybe they would work on some sergers.
This is what my instructor gave me. They're about 3" or 4" with a loop at one end. This is what we used to thread our loopers. I've bought some since...I have no idea where they are now, so guess I need to buy more.