[s-cars] Loose Spark Plugs, the cause?

[S4quat at aol.com]

Bruce,
  Thanks for the feedback.  I know it doesn't happen to everyone, but it does
happen a lot and I wonder if there is a common thread.  I actually had to
retorque my new plugs after about 500 miles and now they have stayed tight
for over 3k miles??  Did I not torque them properly the first time?  Or does
it have something to do with the threads?  Detonation?

Michael