Grizzly stock bolt thread size?

[PepeLapiu]

I don't have any hex nut. Figuring out how to post a pic.

Here is a direct link:
http://s6.postimg.org/vxc6oqj5t/tmp_9531_20150329_2155042114449271.jpg

And here is a forum format link:

image ru

 

[PepeLapiu]

Dammit, it worked!
Anyways, that threaded hole in the center of the back of the receiver is what I assumed the stock bolt would screw into if the 870 is anything like the Mossy 590.
But that thread size is a mistery.

 

[CanAm]

No, you are missing the hex net that stays in pace. The stock bolt threads in to that