air cleaner to filter the dust out of the air inhaled by the engine (an invention that did not originate at Ford but that was still rather novel in 1917). Air cleaning is critical to engine lifespan, even for road vehicles and most especially for farming and construction vehicles (which work in environments where dirt is frequently stirred up into the air). The Fordson carburetor and air cleaner were designed by Holley. In later decades, the water bath would be replaced with an oil bath for better filtering performance. The ignition system was similar to that of the Model T, with a flywheel-mounted low-tension magneto and trembler coils. The ignition timing was manually advanced or retarded with the spark advance lever mounted near the steering column, which rotated the timer. The cooling was by thermosiphon. (In later decades, a high-tension magneto and a water pump would be added.) The transmission was a three-speed spur gear (the three forward speeds ranged from approximately 2 to 6 mph). A worm drive reduction set and a differential made up the rear. The design of the rear was patented for its ease of manufacture and service. Brakes were not provided on early Fordsons, as high-ratio worm sets generally transmitted rotation in one direction only, from the worm element to the gear element, because of the high power loss through friction. To stop the tractor, the driver depressed the clutch. Ford engineer Eugene Farkas successfully made the engine block, oil pan, transmission, and rear axle stressed members constituting the frame. By eliminating the need for a heavy separate frame, costs were reduced and manufacturing was simplified. Ford held a patent on a unit-frame tractor. The rear wheels were fabricated steel, spoked and cleated. The earliest ones were 12-spoke; a 14-spoke version followed. Several models of front wheel were used, including 10-spoked fabricated steel and 5-spoke cast iron. Industrial models also used other wheels designed for specific tasks, including aftermarket wheels. In 1916 and 1917, the name "Fordson" was not yet used as the tractor's make or model name, nor was "Model F". During this period, terms such as "the [real/genuine] Ford tractor" or "the Henry Ford tractor", as well as "the MOM tractor" (because almost all output was going to the British Ministry of Munitions), were used. "The Ford Tractor Company" had already been registered on March 15, 1915 by W. Baer Ewing and Paul