Final answer:
A double reduction helical drive axle uses two stages of gearing with helical gears to reduce speed and increase torque in a drive system. It provides smoother operation and quieter performance than straight-cut gears. The terms 'double' and 'dual' reduction might be used interchangeably to describe this system.
Step-by-step explanation:
A double reduction helical drive axle is a type of mechanical drive system that uses two stages of gearing to reduce speed and increase torque between the drive shaft and the wheels. Contrary to a single reduction axle, which only has one set of gears to achieve this reduction, a double reduction axle incorporates two sets, usually involving helical gears due to their smoother operation and quieter performance compared to straight-cut gears. Neither option c 'Double reduction helical drive axle' nor option d 'Dual reduction spiral drive axle' explicitly matches the information provided; however, they essentially describe the same system with different terminologies. The key aspect of this system is the use of two reductions in series which can result in varying gear ratios including more, fewer, or an equal number of primary and secondary turns.