A metric bolt torque by grade listing is available on RepairEngineering.com and DansMC.com. They provide the suggested torque values for different bolt sizes. In addition to these guides, it is essential to check a shop manual when choosing the right grade of a particular bolt.
There are several factors that define a proper bolt torque specification including the material containing the bolt, material containing the nut and thread engagement. The proof strength of bolts varies depending on their grade and sometimes the diameter. A metric bolt torque by grade listing is essential in determining the right de-rated torque value when adding the lower proof strength materials.