Which statement best describes the purpose of lock tabs or castellated nuts in a torque assembly?

• A. They provide positive retention after torque is set
• B. They indicate the torque value by notch position
• C. They reduce friction in the joint
• D. They replace the need for a torque wrench

Answer: (A)

Lock tabs and castellated nuts provide positive retention after the fastener has been torqued. Once the nut is tightened to the specified torque, a tab or cotter pin is used to lock the nut in place so it can’t rotate and loosen under vibration or cycling. Castellated nuts have slots that align with a hole in the bolt shank; a pin or bent tab fits through that hole and the slots are secured, creating a physical lock beyond simple friction. This ensures the assembly stays at the intended torque and reduces the chance of self-loosening. They’re not used to indicate torque value, they don’t primarily reduce friction, and they don’t replace the need for a torque wrench.