---
title: "Index gear: meaning in gemology"
description: "An index gear is the toothed wheel on a faceting machine that sets each facet's direction around the stone. Each index is one tooth of the gear."
url: https://digitalgemology.com/learn/glossary/index-gear
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Cutting and files

# Index gear

Also called index wheel, index

An index gear is the toothed wheel on a faceting machine that sets each facet's direction around the stone. Each index is one tooth of the gear.

## In more detail

Most of our designs use the common 96-tooth gear; a few use 64 or 120. On a 96 gear, the T73's pavilion mains sit every 12 teeth.

## How we measure it

Each design on our cut pages names its index gear. Our cutting-file check turns each facet's angle and index into a direction and compares it with the 3D model.

## Related terms

- [Facet](https://digitalgemology.com/learn/glossary/facet): A facet is one flat, polished face of a cut gemstone. Its angle and its direction around the stone decide where it sends light.
- [Tier](https://digitalgemology.com/learn/glossary/tier): A tier is a set of facets cut at the same angle, at several index positions around the stone. A faceting design lists its tiers in cutting order.
- [Faceting machine](https://digitalgemology.com/learn/glossary/faceting-machine): A faceting machine cuts and polishes a stone one facet at a time. It holds the stone on a dop at a set angle against a flat, spinning lap.
- [Cutting-file accuracy](https://digitalgemology.com/learn/glossary/cutting-file-accuracy): Cutting-file accuracy states how closely a cutting file's facet angles match the 3D model of the same cut. Each cut page gives the largest angle difference and the mean.

## Learn more

- [Who uses our files](https://digitalgemology.com/about/files)
- [The 3D models](https://digitalgemology.com/about/how-we-measure/3d-models)

[All 328 terms](https://digitalgemology.com/learn/glossary)