As a follow up for torque specifications, here are a few charts listing for most of the common threads and grades. They vary a little probably because of manufacturing variance in alloys. NOTE THE NUMBERS FOR 5/8-18, grade 8.
These numbers have been around since they have had steel.
1-
https://www.fastenal.com/content/mer...ce%20Guide.pdf
2-Torque-Values-for-Common-Bolt-Sizes.pdf
3- Bolt Nut Recommened Torque Table for SAE Grades ...