Antique Singer Treadle Sewing Machine Pivot Bolt Screw and Nut.   This is the same bolt (or machine screw) which attaches attaches both the fly wheel and the treadle to the frame, allowing them to spin.   

Photo is representative of the 9 bolts offered.  You are purchasing one.     

These are original Singer bolts, with antique patina just as removed from the machines.   These are entirely serviceable and can be cleaned and/or restored to whatever level the new owner chooses.  Expect some surface rust, etc. as shown.  Original antique Singer part.