Why do you think it is 53 NM? (For a clean, new, lubricated nut & bolt at least.)
Not even a class 12.9 M8 lubricated is 53 N-M!
Could be as low as 12 N-M for a class 4.8
What is the shear failure torque for a shaft of that size and that material, with 10% margin for stress concentration? Plus if it is not applied as a couple, but as an offset load there is also a pure shear load from the unbalanced applied force.
I am getting 54N.m torque for a grade[ ]8.8 M10X1.5 screw. The equation is T=CDF, were T is torque, C is the friction factor, D is the thread major diameter and F is the tension force. I used a friction factor of 0.15, assuming a lubricated thread. I used 90% of yield strength as maximum stress. This equation assumes a 100%[ ]rigid joint. This may or may not be an adequate description of your application.
Your machine design textbook should fill in any of the blanks I have left.
What is the friction of the bolt head and threads, what is the length of thread engagement, what is the stiffness of the joint, what is the material of the under head bearing surface. All of these are just some of the things that you have to take into account to come up with a seating torque number.
The maximum allowable torque is just a little bit less than the failure torque of the bolt or joint. That number will depend on your application.
