Probably a very silly question, and obvious answer, but I can't quite understand how the size in mm relates to the actual cable. I've bought 2.5 T&E from different sources which appears to slightly vary in size depending on vendor. What does the 2.5 cm actually refer to? The diameter? Radius? And from time to time I come across lengths of cable disposed of in skips. I've got a good 6 metre length of cable that is twin and earth and looks as thick as that used on my cooker, and it says 2 x 10 + 4 on the side. It's 16 mm at its widest. What would this be?