This tool is used for cleaning rust and burrs off parts like the Featherweight hook assembly, loop guard, bobbin case, and tension discs. The rubber honing stick will allow you to quickly and conveniently smooth out and polish any rough spots that would hinder the thread path. Simply take the stick and firmly rub back and forth on the rust or rough spots that need filing down.
The Rubber Honing Stick is made with an abrasive material, and while good for polishing areas on mechanical parts, it should not be used on any polished chrome parts like the faceplate, needle plate, or stop-back motion knob.