The answer is more complex than your question indicates. First not all trucks have left hand thread. In fact, very few today do.. Today, most truck wheels are HUB PILOTED, and have right hand thread. But the early disc rims were designed by BUDD Corporation, with the goal being to distribute brake heat evenly. These rims were STUD PILOTED, but known in the trade as BUDD rims. Budd rims had two nuts on dual wheels, the inner being a stud/nut combination and the outer a nut. All nuts on the drivers side of trucks and trailers were left hand, or reverse thread. This was done to prevent vibrational and centrifugal loosening with the two nut design. Studs and the stud/nut combo were marked L or R on the ends. I will leave it to your imagination what they stand for.

Budd style rims are pretty much obsolete today, for several reasons. First, stud piloted is not as strong as hub piloted. Second, there were more parts to keep track of, and to go bad. Third, getting apart rusted together nut and outer stud was a total pain in the rear, no matter what any expert says in comments. Budd rims were great in their day, and an improvement in heat dispersal from DAYTON, or SPOKE, rims, but their day has come, and gone. Still see them around on someone’s old equipment, but even there most people converted hubs over to hub pilots if they could find bearing compatible hubs.

Now we know 😲😢😒😂