Hi Folks:  Years ago I picked up a 1945 “AMES” US entrenching tool which I have tried and tried to unseize/unlock.  I have sprayed WD40 and placed it in a large vise….but no luck.  I recently saw a YouTube posting soaking a Vietnam era folding entrenching tool in “used” oil for a week and then using a torch to heat up the locking nut/washer …which did work.  Any other recommendations?  This shovel/entrenching tool has probably been locked in place since the 50s/60s…maybe later…which I picked up for very little but I would like to unlock it.  Thank you for looking

Try PB Blaster.  It's more of a rust penetrator than WD40 is. 

A good penetrating oil like PB Blaster or Kroil is your best bet.  Let it soak for a few days if you can.  I've also heard that a 50/50 mixture of acetone and ATF brake fluid make an excellent penetrating oil.  Hitting the nut with a torch will also help, but this may not be an option if there's paint left.  Put a punch on the nut and tap it around the circumference to help break the rust.  A strap wrench may help you get a better grip on the nut and will keep it from getting scratched up.  Good luck!

THANK YOU both for your recommendations