For torqueing nuts and bolts that use lock tabs or castellated nuts, what is the general sequence?

• A. Torque the bolt only
• B. Torque the nut only
• C. Torque the bolt first, then the nut
• D. Do not torque and rely on lock tabs

Answer: (C)

Lock tabs and castellated nuts provide a locking mechanism, but they don’t establish the clamping preload by themselves. The goal is to create the proper bolt preload first, so you should torque the bolt to the specified value to seat the parts and set the initial clamp. Then tighten the nut to its final specified torque to achieve the correct clamp and to position the castellations or tab so the locking feature can be secured. This order helps prevent disturbing preload or misaligning the locking tab or cotter-pin hole; tightening the nut first and then the bolt can alter the preload and compromise the lock. After the final torque is reached, bend the lock tab or install the cotter pin to secure the assembly.