SROBERTLAW200
Don't drive that car!
I don't know if you can find the nut (is it a Grade 8?) at Lowe's but, for sure, your Ford parts counter guy can fix you up.
Do you have a Haynes manual? It has the torque specs for almost all fasteners on the car. The manual is only 20 bucks and it has a ton of good info in it.
HTH,
Chris