These parts include transmissions, oil pumps, pistons, timing gears, flywheels, valves, axles and joints. Smeaton introduced iron axles and gears to water wheels. Brakes are discs on both axles. Both front and rear axles were solid. It was a chair on two wheels with two long shafts fixed to the axles. Later models included locally produced components including&colon; engines, gearboxes and rear axles. These were the front and rear axles, transmission and transfer case . The box could hold of ballast to increase traction on the rear tandem axles. It had a petrol engine and eight torsion-bar suspension axles per side. In order to reduce friction between the wheels and the axles, tar oil was used. There were 13 optional rear axles available, ranging from 2.92&colon;1 through 6.17&colon;1. Each of the bogies had 5 axles, giving a total of 40 axles (80 wheels). Plastic half tubing that protected the axles of the trucks. Some square tapered bottom bracket axles are threaded at the ends and use nuts. A differential gear train can be used to allow a difference between two input axles.