The bolt diameter is 3/8
I put 2 bolts on each cross bar spaced out 4 inches. They are a bit less than 2 inches into the stud.
I wish I would have put thinner bolts but they were out of stock on the next size down and I thought they would be holding a lot more weight so I didn’t use 1/4″ lag bolts.
I did predrill each hole (don’t remember what size I used though).
It’s a 2 story house so I’m worried I used to many large bolts. Please let me know what you think and if you think If there’s anything I can do.