A helical gear unit can be designed as a gear train, a step-up gear unit or as a combination of these. Several bevel gears located one behind the other make up a gear train. One gearwheel drives the next, thus connecting the drive to the output. A gear ratio is only provided by the first and last gearwheels of the chain.
In mulitistage step-up gear units a small gear drives a large gear. This is the first transmission ratio. For the second transmission ratio the large gearwheel of the first stage is connected to a small gearwheel, which then drives the gearwheel of the second transmission ratio. At very high rotational speeds only the first gearwheel rotates at the high rotational speed. The other stages are already stepped down, meaning that a helical gear unit is especially suitable for high rotational speeds.