Torque is a difficult value to calculate accurately, especially for construction fasteners and should be used cautiously. The primary challenge is accounting for environmental factors, coatings, and a number of other variables including surface texture, material hardness, and thread series. In most situations, it is challenging to give reliable allowable torque values for bolted assemblies. For the most accurate data we recommend field testing the intended assemblies using a calibrated torque wrench and a Skidmore-Wilhelm load indicating device to equate actual torque to the desired tension.
The theoretical torque values listed on our site are intended as reference point. This chart only covers products with a published friction coefficient.
In which book I can get the below mentioned formula for Values calculated using industry accepted formula T = KDP where T = Torque, K = torque coefficient (dimensionless), D = nominal diameter (inches), P = bolt clamp load, lb..
@Balaji- We found the T=KDP/12 formula in the technical section of the IFI Inch Standards book. The original text can be purchased from them.