Raphael,
You are correct and wrong. It is part of the Kilfitt multi-mount system, but the thread is definitely DEFINED as a Leica thread Mount. Not because it is intended for Leica screw mount lenses, but the thread designation, 39mm 26 TPI Whitworth, is called LTM.
It is a common misconception that it is the same as M39...which is not true, because M39 has a thread pitch of 1mm, but LTM has a pitch of 0.977mm....almost but not exactly the same.
Yes...these are intended for folks who have the 90mm f3.5, 150mm and 300mm Tele Kilars and the older version of the 90mm Makro Kilar.
It is a very rare item. I paid a premium for this, but then soon realized that I needed capital to start my LF journey. All my Kilfitts are WE lenses, so this was surplus to needs anyway.
Good luck on the Pentacons.......VERY VERY difficult to find one. But, if it helps, I might have an extra WE mount without the rear threads that I MAY be persuaded to let go....not sure I want to sell such rare items yet. Assuming you have WE mount lenses...
Avi