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The nonmetallic materials are wood, rubber, leather, vegetable fibers, and plastics.

Wood. Iron and steel have practically taken the place of wood. There are, perhaps, two reasons for this: first, steel is more durable; second, it is becoming cheaper than good wood because of the scarcity of the latter.

Rubber. Rubber is both derived from the gum of trees and made synthetically. Special compositions of rubber are developed to obtain the properties desired for a particular application. Design engineers should have a thorough knowledge of the properties of rubber—both natural and synthetic. There are several grades of rubber materials varying in the general properties of hardness, flexibility, bonding properties, and chemical resistance. The leading use of rubber on farm equipment is in production of implement tires and tubes. Much rubber is also used in making flat and V belts and for the insulation of ignition wires. Rubber bushings on suspended oscillating components often give an excellent service life and require no lubrication. Disks of rubber to clasp plants are used on transplanters.

Plastics. A plastic material is an organic solid, polymerized to a high molecular weight, that is capable of being molded, usually with the aid of heat, or pressure, or both. There are many groups and types of commercially available plastics. These are sold under many trade names. Certain types of plastics are used for steering wheels, handles, instrument parts, bearings, washers, tubing, battery cases, bristles for brushes, and windows.

Leather and Vegetable Fibers. Leather is largely a belting material. Vegetable fibers are used in brushes, fabrics, and upholstery padding.