AWG, American Wire Gauge, conductor cross-section, CSA, wire size
Cross-section decides current capacity, voltage drop across a length of harness, mechanical strength, and, critically for procurement, which terminal and which wire seal the wire can legitimately be used with.
The two systems in use are less interchangeable than a conversion table suggests. European and Japanese drawings use metric cross-section in square millimetres: 0.13, 0.22, 0.35, 0.5, 0.75, 1.0, 1.5, 2.5 and upward for power. American drawings use AWG, a gauge scale on which the number rises as the wire gets thinner, so 22 AWG is signal wire and 12 AWG is power. AWG 20 sits near 0.5 mm2 and AWG 18 near 0.75 mm2, but the steps between adjacent metric sizes and adjacent AWG sizes do not line up, and "near" is doing real work in that sentence.
The mismatch matters because terminals are qualified against a conductor range, not a nominal size. A terminal specified for 0.35 to 0.75 mm2 has a validated crimp window at each end of that range. Feeding it a wire converted from an AWG drawing without checking the actual conductor area can place the crimp outside the window, and an out-of-spec crimp fails the way it always fails: later, under vibration, in the field.
Insulation diameter is a second and independent variable. Two wires with the same 0.5 mm2 conductor can carry different insulation thicknesses depending on wall type and temperature class, and it is the outer diameter, not the conductor, that decides which wire seal fits.
Harness Code quotes terminals and seals against both numbers, conductor cross-section and insulation outer diameter, so a part that suits the drawing also suits the wire actually on the floor.
Related terms
Terminal / contact
A terminal, or contact, is the metal part crimped to a wire and inserted into a connector housing to make the electrical connection. Terminals are specified by family, gender (pin or socket), wire cross-section range, and plating, typically tin or gold.
Crimp and crimp height
A crimp is the cold-formed mechanical and electrical joint between a terminal and a wire. Crimp height is the measured height of the finished conductor crimp, and it is the main control on whether that joint survives vibration and temperature cycling in service.
Wire seal and cavity plug
A wire seal is a rubber grommet crimped with the terminal that seals the gap between the wire and the connector cavity. A cavity plug seals an unused cavity. Together they give a sealed connector its rated ingress protection; a single missing seal voids it.