Abstract: A method of making a hinge joining two rigid pieces each with top and bottom surfaces, comprising the steps of thermoforming a first piece of rigid plastic material having a first hinge joint; machining a hole with a tubular shape through each of two external surfaces of the first hinge joint; thermoforming a second piece of rigid plastic material having a second hinge joint; machining two keyhole-shaped passage perpendicular to the length of the surface and across the width of the near-end external surfaces of the first protrusion and of the second protrusion of the second piece; inserting a hinge pin through each hole with a tubular shape; and assembling the two pieces with the first hinge joint fitting into the gap of the second hinge.