Did you mean 5/16 or 3/8 a 9/16 is a very big bold if a 9/16 wrench fits it then it is usually a 3/8 bolt...:hello:
No sir, I have a single 9/16" bolt through my motor mount. Which means the head is a 3/4". Long ago, guys would snap a single 1/2" bolt. I didn't want to add two bolts when one larger one would do just fine. It's been 8-9 years and still holds strong.