An Internal Gear could be described as the opposite of an external gear in that the teeth point towards rather than away from the guts, and addendum and dedendum consider reverse positions. Internal Gears provide a small parallel shaft transmission drive with large acceleration reduction. Used with 
a typical spur pinion the ratio is equivalent to that of two exterior gears, but the center distance is much smaller. In cases where it’s important to have two parallel shafts rotate in the same direction, the inner gear eliminates the use of an idler gear.
Internal Gears possess a number of advantages when properly used. One such benefit is reduced sliding actions. The planetary gearbox corresponding working areas of the teeth of an internal equipment and pinion are more almost of the same duration than may be the case with an exterior gear and pinion having the same tooth ratio and tooth duration. Therefore the relative slippage of the teeth is less regarding the internal. This aspect presents among the advantages of using Internal Gears. The sliding action of one tooth over another causes friction; and as friction results in tooth wear, a reduction in the quantity of sliding action is desirable.
Internal Gear drives could be operated with the apparatus in a set position and the pinion rotating along the pitch line, or the gear may be free to rotate with the pinion rotating in a fixed position.
When mating pinions are too close in proportions to the apparatus, interference may result. For that reason, the difference in tooth of the pinion to the gear should not be less than 15.
RUSH GEARS inc. provides standard Internal Gears in STEEL, STAINLESS, CAST IRON, BRONZE, Light weight aluminum, DELRIN and NON-METALLIC (PHENOLIC). We will gladly manufacture made to order Internal Gears to meet your needs.