I am very sorry Banquo, but these nuts do not say anything to me. This time, I am sure that Maestro Grossman will be the man for a genuine expertise. They are not made by SMC.
Steve, I am not sure that the Grivel stacking nut was ever marketed, one more reason to make it so hard to find. The same week I received it from Denis Pivot, there was one sample on eBay.com. It was just incredible, as I had never seen such a nut on eBay before.
I too saw the Laprade Coinceurs Gigogne on eBay recently.
Using that coin for reference, one would think that the pro you're presenting is from the 19th century. I'll bet that at least half the readers under 30 (if there are more than 1) don't know if that's a dime or a quarter.
So we can suspect that Master Grossman knows what these little wonders are… May we have a clue…? Does the “T” stand for “Tested”…? As I am not very proud not to have any idea of what these single wire nuts could be, I have post a photograph of the Master for the HB New Curve nuts. Unfortunately these HB nuts were never marketed...
Mirror, my beautiful mirror, am I still the “Maestro”…?
I actually don't know the source of these nuts but I suspect that they are Black Diamond by the "T" for tested and that the heads appear to be the same material that Steel Nuts are made from. Prototypes by the lack of a stamp which were likely limited by the inability to get sufficient solder penetration into such a relatively large cable cross section. An interesting design to say the least with the offset tapering on the head shapes.
No worries Maestro, your lofty status is never in doubt.