AWG= American Wire Gauge
As the number increases, the size if the wire decreases. 28 AWG is fairly small wire, about the size of a small broom straw. As a size comparison, car battery cables are in the 4-6AWG range, 110 volt 15amp house outlets use either 12 or 14AWG wire. Can purchase at Radio Shack and other electronics outlets.
Dialtone
IDE cables (for connecting hard drives to motherboards in computers) - anyone any idea what AWG they are? (i suspect measuring the diameter of the wire may prove a bit tricky!!)
I suspect they are in the 26-30 ga. range, but the last IDE cable I made up had multi-stranded conductors. Made stripping and soldering it to a pcb a real headache.
Dialtone
As already mentioned, AWG is 'American Wire Gauge' the UK uses (or at least used to use!) SWG 'Standard Wire Gauge' - as with gallons, tonnes and many other things the Americans changed it slightly. A quick google found this site with a conversion chart https://www.simetric.co.uk/siwire.htm.