I need to know the size of this bolt ASAP!

I measured the bolt

5/16" Shank
20 Thread
1" Underhead Length

Is what I got from the factory bolt.....

I NEED to find some ARP SS bolts that are this size but can not find any?

They only seem to have 5/16-18 and 5/16-24, but do have 7/16-20...am I missing them at Summit?

I took my differential cover bolt which is 5/16-18 and it WOULD not screw into the water pump pulley hole, also took a 5/16-24 and also did not work, so I can't be measuring wrong? Or am I? And if I am please tell me the size so I can get some ARP bolts already.

Thanks
Take care

 

they are 5/16-24

if that does not work, you somehow managed to get a metric threaded flange, which i didnt know existed .

 

I am using the Stewart Stage 2 Water Pump if that changes anything. I checked Stewart's site but they did not list the information.

I used these bolts ARP-722-0750

 

Well, I globed anti-seize on them and bolted them in, it was VERY VERY hard to get them bolted all the way down. I had to have 1 person hold the pump pulley while I bolted the bolts in. 2 went in fairly okay, but the other 2 were like bolts from hell.

I unbolted the bolts and no threads were ruined and no signs of cross threading. They went back in very tightly but a little better than the first time.

I think this was all because they are SS bolts...

 

Not sure if anybody else has had this problem or not. I just went to install mine tonight, and broke one bolt off in the flange and the others stripped out. I also have the stewart stage 2 pump.

 

Gonna bump this old thread because I’m running into the same issue except with a generic AutoZone water pump for a 92 rs camaro. Everyone online says 5/16-24 so I ordered 5/16-24 arp bolts and the thread spacing is too tight. I tried a 5/16-18 bolt and the threads were too course. I have one original pulley bolt that threads in fine and doesn’t match either thread counts. Counting the threads myself gives me 5/16-20. If it’s truly a 5/16-20 bolt then why does everywhere online pertaining to thirdgens and small block chevys in general say it’s 5/16-24?

 

The WP has 5/16"-18 ("standard thread") holes. The nuts that hold the clutch on are 5/16"-24 ("fine thread").

Generally they put studs in the WP that have the 2 different threads, the "std" to screw into the flange and the "fine" for the nuts. Most experienced people will put 2 of the nuts on em and use a wrench on the bottom one to pull the studs out out so they can re-use em. Other people return their core with the studs while still screwed into it when they buy a new WP, and don't realize that they just sodomized themselves until it's too late. But all is not lost... you can get em on cards in the Help! section at most parts stores. The same thing is also used as carb studs, you can get the exact same thing under the different name and they'll work just as well.

They are NOT 5/16"-20. There's no such size. The threads on 5/16" hardware are either 18 or 24 per inch.

Your issue has NOTHING to do with "SS", "Stewart", or any of that, like the other guy thought. It's simply that you don't have the right hardware. Get the right studs and it all will just jump right together.

 

I ended up chasing the threads with a tap and the bolts went right in, the 5/16-24 at least threaded in somewhat prior to me chasing the threads compared to the 5/16-18 which is why I chased with the 24 thread. All is well

 

I had the same problem.
The water pump pulley bolts are metric they are m8-1.25 x 16mm long.
Auto Zone has them.