I agree Craig and I've done this myself using both hex-heads from donor bolts and also new 'hex stock'. I had to make my own 3/8 x 24 nuts for New Departure rear axles, found they are actually 3/8" plus .010. I was able to buy a new tap in the correct size. The way I use it attempting to extend its life, I first drill the hole then tap with a standard 3/8 x 24 tap size, then I tap again with the 3/8 +.010 " tap.
I found some old axles are well used/worn and don't even need the plus .010" nuts, standard 3/8 x 24 nuts will work fine.