RE: FG 1/5 scale drag car
The rear axle is 1/2", but a hard-coated, precision ground aluminum shaft I got from McMaster-Carr: #5911K23. The halfshaft is 10mm, to fit all the FG gears and pulleys, which as you know, are all metric. (#1482K11).
I kept a record of most of the part numbers and sources for everything, anything you want to know... I probably wrote it down somewhere.