The Jew's harp, sometimes called by its more politically correct name, the Jew's-harp, is a simple musical instrument which uses your mouth to echo the sound. It relies on a rigid metal frame and a small metal reed which players flick to create vibrations. You can add some personal twists to the instrument, but the basic shape and design are fairly simple to make if you have the right tools and equipment available to you.
Open the ends of the split pin to about a 30 degree angle.
Insert the iron core or drill bit into a clamp, and bend the split pin around the core so it creates a widened circle. Use pliers to shape the split pin. Bring the ends of the pin back around, so they're less than 1/2-inch apart.
Grip an arm of the split pin and twist it about 60-degrees. Repeat with the other arm so they create a flatter surface.
Cut a thin strip of steel spring off. Make the strip about five inches long by about 1/4-inch wide.
Clamp the spring strip using shims to both straighten it and prepare it for grinding.
Grind the spring with a circular motion on a block to smooth the piece.
File the spring down so it forms a point. File the rear of the spring to a curve, so you don't catch yourself on a sharp edge.
Bend the last one inch of the spring straight up, then curl the pointy tip around itself into a loop. This gives you something to flick later.
Place the split pin in the clamp again, and file both arms to a slight point.
File the tip of the circle down to create a slot for the pin. Make the slot no wider than the pin is, and about 1/16-inch deep.
Push the spring into the slot, and then hammer it into place. Place the hardened wire over the spring so you don't damage the spring while hammering it into place.