Almost a complete disaster

He didn't have correct torque on them. It's irrefutable.

 

I would also claim Bull S on his claim of watching the guy use a torque wrench. Even when the torque wrench is out of spec they are rarely ever out far enough to have this happen.

Be thankful he is willing to pay for the damage and that you caught it before it became a disaster.

 

Torque wrenches have test dates and the shop owner should have a record of that, but my bet is he doesn't.
Let him pay like he said he would and move on.

 

Truckstop shops have written on the receipt that wheels should be retorqued after 100 miles. I've always believed that's to cover their liability in case the mechanic didn't torque correctly. I never retorqued and never had a problem.

 

Could be studs were previously stretched from over torque.
Mounting surface of assembly had crud on it somewhere causing bad seating issues.
Wheel was not seated correctly over hub. Common with this new design.
Lug nuts where not replaced with new ones when put one.
Torque spec on them are 500 ftlbs. And nuts are are supposed to be replaced after a couple uses.
Wheel offs with hub center style wheels has been astronomical. Studs are two small for two wheels. They are hard to seat and the nuts do very little clamping when the wheels just float around the studs. Torque needs to be checked more frequently but never is.

 

It is possible the shop torqued the nuts. When they check with torque wrench, if the nuts don't move with torque wrench. How tight are the nuts?
The nuts could have been over tightened, stretching the bolts.

 

Years ago, I know someone who had wheels under torqued and and a wheel came off around 1k miles later. All other positions were undertorqhed as well. I have a hard time believing stretched threads and/or improper seating because of corrosion on hub face and/or wheels a wheel wouldn't stay on more than 12k miles if torqued right. I've done my own tires for 20 years and have let slide corrosion when in a hurry. I would fix tires in a parking lot using air from the truck and wouldn't spend time chasing threads and cleaning hub face.

 

1200 miles

 

When a wheel comes off and causes an accident one of the first things an investigator looks at is the amount of corrosion on the hubs. They then will check for damaged studs. Stretched, bent, out of round, and flattened threads. Industry rule of thumb says if two or more studs fail it is due to over stretching. This is why they highly recommend replacing the studs and nuts on both sides of a bad one even if they look good.