The unit consists of a metal base plate with a fixed axle and a rail made of steel. Two further axles can be clamped to the rail in any position. This benchtop unit conveys the relationship between the number of gear teeth on spur gears and the transmission ratio of gear trains. In this way it is is possible to construct one and two stage gear trains with any combination of gears. Drive pins couple the gears. Four plastic gears are included with the unit. A plastic box is used to store the parts not in use. By undoing a locking pin, the rail can be swivelled around the fixed axis providing a demonstration of planet gear trains.
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