Hi John and welcome,
Can you explain more what you mean by an Indexer, I know of three types and there may be more. My example pictures are from arceurotrade's website apart from the Dividing Head, which is from Wikipedia.
1. A stand alone spin indexer where a pin engages in holes in a disk:
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2. A stand alone Rotary Table where a handle drives a worm gear allowing angles to be traversed. Can mounted flat or vertical.
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3. A Dividing Head. Also stand alone, usually with a Spin Indexer disk, plus a Rotary Table worm drive and also with the holed disk with brass 'clock hands' and drive handle arrangement at front. Divider Plates are an important aid to turning accurate angles as when making gears.
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There are further variants, in particular I wonder if you mean a spin indexer attached to the lathe spindle, which allows work in the chuck to be held in a known position while – for example – horizontal splines are cut. These are far more common on woodworking lathes, where they are used to add decoration as when making pens. There was a thread a while ago on this forum about a metal-working lathe that appeared to have been factory fitted with a spindle indexer. It attracted a lot of interest because it was so rare! As can be seen from the photos, dividers and rotary tables are more often used on a Mill than a Lathe.
Rotary Tables can usually be fitted with Divider Plates as an accessory. Or, it's becoming increasingly common to drive rotary tables with a stepper motor and computer-controller that replaces the Divider Plate/Clock Hand unit and does all the sums for you (and doesn't lose count when the phone rings!)
If you can say what type of cutting operation(s) you want to do, then loads of experienced machinists on the forum able to help.
Apologies if I'm preaching to an ex-military armourer who already knows all this stuff!
Dave