The gear knob, or shift knob, is what a manual transmission car has on the top of the shifter rod. These are usually colour matched to the rest of the car's interior. The gear knob is easily twisted off and replaced with an aftermarket one if you so desire. Making your own gear knob is easy, as it is only a round piece of material with a cylindrical opening on the bottom where the thread from the shifter rod can catch.
Turn off your vehicle and pull the emergency brake up to secure the car in its spot.
Twist your manual gear knob counterclockwise and pull it off. This will reveal the shifter rod thread.
Measure the shifter rod's top and drill a vertical recess into the material you want to make the shifter knob out of with the same diameter of the top of the shifter rod. This can be wood, plastic or any other rigid material.
Insert the plastic cylinder insert into the recess you made previously. This will act as the thread. As you turn the new shift knob onto the shifter rod, the threads from the rod will make threads in the plastic, holding it securely.
Twist the gear knob onto the shifter rod clockwise to tighten it onto your vehicle.