The theoretical part is focused on evaluation of chosen ?essential? plastics used in the car industry. The principles of construction and proportioning of plastic components, basic conception of injection moulding and measuration follow. Another section of the theoretical part presents a summary of possible CAD systems, which are used. The practical part is focused on a particular plastic moulding. It includes the main description of a component with its material choice in dependence on the component function. Another section contains evaluation of the component complexity from the viewpoint of moulding, and a possible substitution of constructions, which could be productively simpler, is shown. The whole thesis is completed for better lucidity by pictures, drawings, and mechanical drawings.