Used to snood a hook to a line. As almost all the hooks on the shelves are eyeless, little tools like these are popular and very handy for tying on small hooks. In short, a hook is laid along the stainless steel piece at the end and held in place with your thumb. One wrap is made around the very end of the tool (which has notches) then e.g. 5 times around the hook shank, and back through the first wrap, then pulled tight. As always, easier done than said.