Torque Table & Equations

torquetable

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