Internal gears feature teeth generated on the internal diameter of a cylinder, while external gears have teeth on the outside diameter. Among various gear types, only spur and helical gears can be manufactured as both internal and external configurations.

Internal gears provide high power transmission within compact dimensions, making them ideal for space-constrained applications. They are commonly referred to as ring gears and are extensively used in planetary gear systems.

• Low vibration operation for smooth performance
• High speed reduction ratios in compact designs
• Cost-effective gear train solutions
• Compact center distances compared to external gears

Planetary gear transmissions are widely used in robotic arms, hybrid vehicle power systems, and turbine generators. Helical internal gears are employed in internal gear drives, differential systems, and planetary drives, requiring specialized housing designs.