- Fastener Torque: determining the proper torque is the most difficult problem in fastener installation
- The coefficient of friction between mating threads
- The coefficient of friction between the bolthead (or nut) and its mating surface
- The effect of bolt coatings and lubricants on the friction coefficients
- The percentage of bolt tensile strength to be used for preload
- Once agreement is reached on item 4, how to accurately determine this value
- Relative spring rates of the structure and the bolts
- Interactions formulas to be used for combining simultaneous shear and tension loads on a bolt (should friction loads due to bolt clamping action be included in the interaction calculations?)
- Whether "running torque" for a locking device should be added to the normal torque

- Torque tables such as listed in the appendix may be used. Alternatively, the following equation may be used for quick calculations:

\( K = \left( \frac{d_m}{2d} \right) \frac{\tan \psi + \mu \sec \alpha}{1- \mu \tan \psi \sec \alpha}+0.625 \mu_c \)

Where,

\( d_m = \) thread mean diameter

\( \psi = \) thread helix angle

\( \mu = \) friction coefficient between threads

\( \alpha = \) thread angle

\( \mu_c = \) friction coefficient between bolthead (or nut) and clamping surface