Gear. Computer-aided design (CAD) of a gear from a car or lorry. Gears allow rotational motion to be transferred from one component to another. The blue cylinders lining the inner part of the gear are roller bearings, designed to reduce friction between the gear and its fittings. CAD is a tool by which objects can be completely designed in three dimensions, and tested before they are built. It saves time and money, as incorrect designs can be corrected quickly and easily. The data from the computer can be fed into a mechanical production line, and the object can be built automatically.