Below is a list of Planetary Gears manufacturers from North Billerica, Massachusetts. Planetary gears, or epicyclic gears, consist of three or more outer gears, referred to as planet gears, which revolve around a central gear, also known as a sun gear. The allusions to the solar system refer to the design of the planetary gear; all of the gears in the planet gear are in one plane and are grouped around each other much like the planets surround the sun.