I have a trio of Hardinges plus an Elgin (just so they don't have to be taken off each machine and swapped around so much
) Unfortunately, none of mine have the gear drive input provision.
As noted, the basic Hardinge is 4:1 ratio, and with the stock size plate and stock hole & pin size*, 90 is the max, 1°/ hole (360° in four cranks, to drive the spindle once round). I find it an extremely fast and convenient accessory for routine dividing tasks, especially since it takes all the same internal and external spindle nose tooling as the lathe including chucks, faceplates, 5c collets, and 5c step chucks with external ring closers. The heads have "Zerol" gears and no backlash, so it is easy to go backwards and forwards for dividing.
However, it take more numbers in the plates to get all the division options from 2 - 360; and some divisions such as 125 (needed to engrave dials for 8 pitch leadscrews) are not possible no matter what count you might try to drill in a spare plate. (While a 125 hole ring would do it, I would like to see the solution to doing that practically on the hardinge-size components, or a larger plate without deleteriously modifying the mounting system)
All that said, a Hardinge with the leadscrew driving provision, is 40:1 as far as the gear ratio. The input shaft is 10:1, x the 4:1 from the hand crank shaft that it inputs to by worm drive. The actual dividing possibilities are still governed by the plates on the 4:1 shaft.
*stock hole and pin size (in the dividing plates): I do have one plate that was shop drilled for, IIRC 100 holes at the extreme rim, with a drill that is smaller than the stock pin. Presumably "whoever" used it for a certain purpose with a pin ground to match, when needed.
smt