The ULTRA TEC Mast comes with a 96 Index Gear (the most often used). Faceting designs specify the Index Gear. The 96 and 64 Index Gears cover about 80% of published designs. Changing Index Gears takes only a few minutes. The symmetry of a design depends on which numbers divide evenly into the available number of teeth on the Index gear. For example, a five-sided design will use an 80 Index Gear. A three-sided design with use a 72 or 96 Index gear. And so on. Why does a designer choose one or another when both will allow the same number of sides? Well, the more teeth, the more subtlety of design is possible. Index gears available are: 32 – 64 – 72 – 77 – 80 – 84 – 96 – 120.