Torque Table & Equations
Download a PDF version of the chart here.
The above torque table was developed and simplified for marine applications, and is based on material strength.
Torque Table Equations
First, the units:
$$TPI$$ Threads Per Inch
$$d_{nom}$$ Nominal diameter
$$A_t$$ Tensile Stress Area
$$F_y$$ Yield Strength
$$F_i$$ Preload
$$S_p$$ Proof Strength
$$K$$ Coefficient of friction (=0.15 for lubricated screws)
To determine Preload:
$$F_i=0.75F_p$$ for non permanent connections1.
$$F_p=A_tS_p$$
$$S_p=0.85F_y$$ for proof strength
To calculate bolt torque:
$$T=KF_id$$
Which can also be written as:
$$T=(0.15)(0.75)A_t(0.85)F_yd_{nom}$$
References
- Shigley’s Machine Design, 1998. p. 427 (Eq. 8-30)
- Shigley’s Machine Design, 1998. p. 423 (Eq. 8-27)