What Torque for #8 Bolt?

#8 torque in practice

A dry #8 Grade 5 bolt takes 2.44 ft·lbs (3.31 N·m) on the coarse 32 TPI thread. Oiled, that falls to 1.83 ft·lbs; the dry figure on an oiled bolt overshoots the intended clamp load by about 33%. Grade 8 needs 3.44 ft·lbs (41% more), and the fine 36 TPI thread raises the Grade 5 figure to 2.57 ft·lbs.

#8 is a machine-screw size. SAE J429 formally starts at 1/4", so the grade figures here apply the same proof stress to screws sold as Grade 5 or Grade 8 equivalents; check the supplier's rating. The torques are small enough that an in·lb torque screwdriver or a 1/4" drive wrench is the right tool, and the female thread in a tapped part will usually strip before a Grade 5 screw breaks.