Sentence:  The binder cuts the wheat down and bundles it into a sheaf. The sheafs are then stooked into a field to dry. A metal plate on the binder would have originally been made of wood, but the fact that this machine could automatically tie string was at one time state-of-the-art. ¶ “That <WSD>knotter</WSD> was a marvel of its time. I mean this is a huge technology jump to be able to have a piece of mechanical machinery that actually tied a knot.” 
Meaning of the word marked with <WSD> tags:  A machine or device that makes knots.