The 256 index — also referred to as the 256-tooth index — is a faceting index gear divided into 256 equally spaced positions around its circumference, yielding an angular resolution of 1.40625° per step. It represents one of the finer subdivisions available on modern faceting machines and is the preferred choice wherever a design demands close angular control that lower-count gears cannot reliably deliver.

What an Index Gear Does

On a faceting head, the index gear is a toothed wheel — or, on digital machines, an encoded disc — that locks the quill (the spindle holding the dopstick and stone) at precise rotational positions relative to the lap. Each numbered position on the gear corresponds to a specific azimuthal angle around the stone's axis. The cutter selects a position, engages the detent or stop, and grinds or polishes a facet; rotating to the next prescribed index number then places the stone at the correct angle for the adjacent facet. The total number of teeth therefore determines how finely the circle can be subdivided.

Angular Resolution and Practical Significance

Common index gears carry 32, 64, 96, or 120 teeth, with 64 and 96 being the workhorses of standard commercial cutting. A 96-index resolves to 3.75° per step; a 64-index to 5.625°. The 256-index, at 1.40625° per step, offers more than twice the angular granularity of a 96-index. In practical terms this means:

• Facet meets on high-pavilion-count rounds (64-facet, 80-facet, and beyond) can be positioned without resorting to half-step interpolation or mechanical compromise.
• Emerald cuts with multiple tiers of break facets, where the angular spacing between facets in each tier is non-trivial to divide on a coarser gear, become straightforward to lay out.
• Custom and competition fantasy cuts — designs that deliberately exploit unusual symmetry groups or asymmetric optical effects — can be executed with the precision their diagrams specify.

Many published cutting diagrams written for the 256-index use index numbers that are simply not available on a 96- or 64-tooth gear, making the gear a prerequisite rather than a luxury for those designs.

Compatibility and Machine Fitting

Index gears are not universal. Each faceting machine manufacturer specifies the arbour diameter, detent geometry, and gear diameter that fit their heads. A 256-index must be sourced or machined to match the specific machine — whether a Graves, an Ultra Tec, an Omni, a Facetron, or a custom-built unit. Some manufacturers supply 256-tooth gears as optional accessories; others leave the market to specialist machinists or the amateur community. Digital faceting heads, which encode position electronically rather than mechanically, can in principle offer 256-position (or finer) indexing through firmware, but the physical detent gear remains the standard on most machines in active use.

Who Uses the 256 Index

The 256-index is most commonly encountered among advanced amateur cutters working in the competition circuit — particularly those cutting for organisations such as the American Federation of Mineralogical Societies (AFMS) or the Faceter's Guild — and among professional custom cutters producing bespoke stones for designers and collectors. Standard commercial cutting operations, which prioritise throughput and work from a limited repertoire of established designs, rarely require it; a 96-index covers the vast majority of round brilliants, ovals, cushions, and standard step cuts encountered in everyday trade. The 256-index is therefore a specialist tool: unnecessary for routine work, indispensable for the designs that demand it.