That's what I would have guessed, AWG. Also, you can measure diameter or cross sectional area, but seems to me you have to measure diameter to calculate cross sectional area??? Some charts give both, but most give diam. Use whatever your chart says. That's if you have wire you don't know the size of (I measure the diam of wire from time to time, damn sloppy techs).
Also, you don't use 'hookup' wire. They want magnetic wire, which is copper with a shellac type finish. Hookup wire has plastic insulation which is thicker and will distort the diam. of your coils.
Mike is right on the money. The wire is called magnet wire, enameled wire or Formvar insulated wire. You didn't tell us where you live, so I can't suggest a possible source. The 1/8 diameter means the diameter of the air core. I'd use the flutes on a 1/8 drill bit to wind the coil. It will remove easily.
That coil would be about 470 nH if that helps at all. So, combined with the 22 pF capacitor in the collector tank, I assume this is designed for 49 MHz?