I need to rewire some bits of my cellar. I want to use conduit so I can run
power, phone and lan.

I think I'll be able to squeeze it all into 20mm, the question is where to
get it, and the metal surface mount sockets?
I was thinking about screwfit but I have a feeing it might be a lot cheaper
elsewhere.

Also how does one join the conduit to the boxes? And what about junctions?

TIA

D