in case anyone else has this issue, the bolt is a 7/16"x20 thread, with a 17mm head, and from what I can tell, it is an SAE grade 5 fastener (standard spec for seat belt bolts). Yes, a metric headed, english threaded bolt. It has a 14mm diameter, 10 mm long shoulder and is 38mm long (1.5")
That makes no sense at all. I'm not sure I'm following your measurements here. Maybe I'm just misreading it
You say both 7/16" and 14mm for the diameter of the bolt? That's not possible. 7/16" and 11mm would make some sense as they are very close. 7/16" and 14mm are not. 14mm is close to 9/16".
US fasteners are indicated as diameter - thread count (threads per inch) x length. Metric fasteners are indicated as diameter x thread pitch (distance between threads in mm) x length. So you have either a 7/16-20 x 1.5 bolt OR a M14 x ?(most likely 1.5) x 38 bolt. But those bolts are not close except in length.
What did you measure to get the 7/16" and the 14mm readings? You have a 7/16" what? Root (aka minor diameter)? And a 14mm shank or thread (aka major diameter)? That could be but I somehow doubt that you measured the root.
I'm just not following your measurements here. It's either SAE or metric, not both. If it is a 7/16"-20 x 1.5"(length) bolt, fine. If it is an M14 x 1.5 x 38 bolt, fine. But you can not have a 7/16-20 bolt with a diameter of 14mm, etc.
And my bolt is a Class 8.8 which is similar
to a SAE Grade 5 bolt. Not exact but close. You will need to look up the torque value for the particular bolt that you have chosen to use.