Like the title says, what's the difference? They are both 7/16 x 20 left hand thread.
Big Gear Head has cautioned me to get bolts with a 3/4" head as opposed to the 11/16" head bolts I have now.
I have searched high and low for an answer to this. If there is any difference, it could only be length, or possibly shoulder width.
I would hate to unbolt one that is already torqued down to measure it, but I could. Finding a torque wrench that reads left handed is tough around here!

 

If I can remember it tomorrow I will check. I have a 9 bolt diff sitting on my bench with the bolts in it and I have a box full of bolts from the 7.5. The problem is getting me to remember to check.

 

Lol, I'll remind you. Thanks again my friend!

 

Short term memory bump
Don't forget to measure those bolts B.G.H!

 

I actually remembered to check them. I have pictures that I can email to you if you want them. I can send them to anyone if they want to post them on here, but I can't post them.

The bolts have the same threads and are almost the same length, but the 9 bolt ring gear bolts have a 5/8 head on them and the 7.5 bolts have a 3/4 inch head. The 7.5 bolts would work in the 9 bolt if you had a very thin wall socket to tighten them, but a regular socket won't work. There just isn't enough room around the bolt head to get a 3/4 inch socket on the bolt. The ARP 12 point bolts might work just fine because usually 12 point heads are smaller than the 6 point heads. The 9 bolt ring gear bolts also have a longer shoulder than the 7.5 bolts. I don't think that will make any difference.

 

Interesting, if the 9bolt heads are 5/8" from the factory, do you think they would back out?
After looking at the original bolts and the ones I got from Ratech, the originals have a flared base at the bolt head while the Ratech bolts look like a regular machine bolt.
I can see where there would be a huge difference in grip when tightened.
Question now is what should I use? I have a complete set of original bolts (I know I'm not really supposed to re-use them, I have the Ratech bolts, which even if I added washers don't look like they would hold properly, I could spring for the ARP 12 point bolts with washers and hope the washer lifts the bolt head enough to get a socket on them. What do you recommend?

 

I would use the old bolts 100 times before I would use the Ratech bolts. The large contact surface under the head of the original bolts is what will keep them from getting loose while in use.

 

Guess I'll wire brush them up and see how they look then.