Here in Austria I've only seen 6mm2 solid. Was real tough wrapping that around the terminal screws of ca. 1913 Diazed fuses (I was installing a new feed to our apartment). In another place I used 10mm2 stranded for the same purpose. Pretty ridiculous for 20A main fuses. The wire I'm talking about had about 5 strands looking like 1.5mm solid wires each.
No, U-boats look like wirenuts with screws. You mean strip connectors or choc blocks (well, they don't look _that_ much like chocolate, but I can see the ressemblance).
On the cut strands: I just took apart a Schuko plug (the Kopp rubber type that'S used for garden stuff, etc). The strands were just stuffed loosely into the terminals, not even twisted. The wire ends were stripped far too long, abou 1/2 cm of copper was sticking into mid-air. I guess the screws only gripped maybe 5 strands of the 1mm2 cable. The blue wire was part black and when I took the plug apart the sheathing of the flex (it was only a short piece, had been cut off) came right off. Obviously never heard of a strain relief.
The only instance where I've seen flex inside walls was the infamous 0.75mm2 zip cord (Zwillingsleitung) used to feed an extra receptacle.
