Hanger bolts are threaded at both ends, and you'll need them to connect the knob to the wall. To find the correct size, take the screw that comes with the knob to a hardware store and ask for a match.
Resources: Liberty White birch knobs, in Natural, from homedepot.com. Paint (on wall), in Hosta, and paint (on knobs), in Persimmon Red, Tidewater, Awning, Bay Leaf, and Beach Grass, by Martha Stewart Paints; homedepot.com. 24k Pure Gold spray paint, by Design Master; dmcolor.com.