I have 1" billet spacer/adapters on my coupe and my son has 1 3/4" spacer/adapters on his sedan. Mine have been on there for over two years with no problems. My son learned the hard way that you should install these things with a torque wrench - he lost a wheel one afternoon when one of the spacers worked loose and sheared all five lug studs off the right rear axle! My advice: install the spacer/adapters onto the hubs with a torque wrench at a minimum 130 lbs/ft. If you are using spacers over 1" thick, you may want to use blue loc-tite on the axle studs. Check them periodically to see if everything is staying tight. If you ever feel any sudden or unexplained vibration that stops when you stop rolling, check for a loose spacer/adapter.

These billet things are a lot better than the crappy old cast adapters we had in the '70's...