The 192 index — also referred to as the 192-tooth index — is a faceting index gear divided into 192 evenly spaced positions, yielding an angular increment of 1.875 degrees per division. It represents one of the finer graduations available in precision gem faceting, occupying a specialised niche above the far more common 96-tooth gear and well above the entry-level 64-tooth. Its primary value lies in enabling symmetry systems that cannot be cleanly executed on coarser indexes: specifically, designs requiring 24-fold, 32-fold, or 48-fold rotational symmetry, all of which divide evenly into 192.

Context within the index gear system

Index gears are the toothed wheels mounted on a faceting machine's spindle that lock the gemstone into discrete rotational positions as each facet is cut. The number of teeth determines both the angular resolution and the range of symmetry systems the gear can accommodate. The 64-tooth index, standard on many entry-level machines, provides 5.625-degree increments and supports 4-fold, 8-fold, and 16-fold symmetry. The 96-tooth index — the most widely used in serious amateur and professional faceting — offers 3.75-degree increments and cleanly supports 6-fold, 8-fold, 12-fold, and 24-fold symmetry, covering the majority of round brilliants, ovals, and standard fancy shapes.

The 192-tooth gear doubles the resolution of the 96, making it a natural extension for faceters who have reached the limits of what a 96 can express. Because 192 is a multiple of 96, every position available on a 96-tooth index is also available on a 192, meaning the 192 is a strict superset: any design cuttable on a 96 can be reproduced on a 192 without modification to the cutting diagram.

Symmetry systems enabled

The practical advantage of the 192 index is best understood through the symmetry divisions it unlocks cleanly:

• 48-fold symmetry (192 ÷ 48 = 4 positions per repeat) — used in highly complex round designs with very large numbers of break or split facets.
• 32-fold symmetry (192 ÷ 32 = 6 positions per repeat) — supports certain fantasy and competition designs not achievable on a 96.
• 24-fold symmetry (192 ÷ 24 = 8 positions per repeat) — also available on a 96, but the 192 allows additional intermediate facets within each repeat.
• 16-fold, 12-fold, 8-fold, 6-fold, 4-fold, and 3-fold symmetry — all supported, as these divide evenly into 192.

Notably, the 192 does not support clean 5-fold or 10-fold symmetry (192 is not divisible by 5), so pentagonal and decagonal designs still require a dedicated 80- or 360-tooth index, or careful interpolation.

Applications in the cutting room

The 192 index is most commonly encountered in three contexts. First, competition-grade faceting: international and national faceting competitions reward optical precision and symmetry, and the finer angular control of a 192 can reduce cumulative positional error across stones with many facets. Second, fantasy and designer cuts: complex proprietary designs — particularly those with layered pavilion architectures or numerous break facets intended to maximise light return in unusual ways — are often drafted specifically around the 192's division set. Third, precision re-cutting: when an existing stone with a non-standard facet count must be re-polished or corrected, the 192 offers enough resolution to meet the original facet positions that a 96 might straddle awkwardly.

For everyday commercial faceting of standard rounds, ovals, cushions, and calibrated fancy shapes, the 192 offers no practical advantage over the 96 and its additional positions go unused. It is therefore regarded as an advanced or supplementary tool rather than a replacement for the standard gear set.

Availability and machine compatibility

The 192-tooth index is produced by several faceting machine manufacturers and aftermarket suppliers, though it is stocked less routinely than 64- or 96-tooth gears. Compatibility depends on the machine's spindle diameter and indexing mechanism; most machines designed to accept interchangeable gears — including those built around the Graves, Facetron, Ultra Tec, and Raytech-Shaw platforms — can accommodate a 192 index manufactured to the correct bore and tooth profile. Faceters should confirm dimensional specifications with their machine's manufacturer before ordering, as tooth pitch and hub diameter are not universally standardised across platforms.