Warm up polymer clay by squeezing it in your hand and rolling it back and forth. As the clay warms up, it will become pliable and easy to shape.
Sculpt the clay into a knob. Press a dowel rod into the back side of the knob to clear a space for a 1 1/2-inch threaded bolt. Remove the dowel. Press a nut for the bolt over the dowel hole so that the hole is centered, and the side of the nut is flat with the base of the knob. The nut should be surrounded by clay. Remove the nut, but don't disturb the impression. Repeat for every knob you intend to make.
Place aluminum foil on a cookie sheet. Position the knobs on the foil. Bake the polymer knobs in a 225-degree oven for 20 minutes. They will harden in the oven. Allow the items to cool completely.
Sand the knobs to remove any imperfections. Glue the nuts into the underside of the clay knobs. Paint the knobs with acrylic artist paint, using a small artist's brush. Allow the paint to dry. Spray the knobs with three to four coats of acrylic clear coat for a nice finish.