El Chaba. Thank you for that thorough description. I am running friction with a Suntour Cyclone 6000 r.d., so I am not anticipating any efficiency-reduction if I install some of the three-spline cogs (of either era). I thought I got lucky with a N.O.S. Maillard 14T that I had, but the mounting threads, as you can see, are on the outside of the mounting collar, which, of course, differs from the A.R.I.S. high cog.