I'm assuming that they are torque prevailing nuts because, as you said, this wasn't required from the factory. IIRC from my install, the nuts have a very slight oval shaped to them. This increases the friction btw the nut and bolt which also prevents the assembly from loosening. Because of this, they are commom on steering and
suspension pieces (strut to spindle nuts for example). Typically, torque prevailing nuts are one time use.
I know I've read (somewhere) that it's recommended to replace the factory hardware when changing
LCA/UCA's. Can't find it know though. Mine (and a friends) were installed using a torque wrench, both of them loosened up over time. This created a squeeking/creaking noise, some slight clunks, and the rear of the car felt a little loose. The problem returned at least three times. A re-torque fixed it everytime. The last time I used loc-tite and the problem has not returned.
Grn92LX,
If you have aftermarket
LCA's along with a creaking/squeeking noise, I would do a quick re-torque first. My noise was so bad, I thought the bushing where worn out.