How to make sure steering box doesn't loosen up?

FISHBREATH said

Also, be aware that torqueing down bolts beyond specification will stretch the bolts and loosen the threads over time.

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Uh, no. The bolt doesn't stretch in the threaded part, it stretches in the part that's not in the threads. That's where the tension is.
Now the manufacturers are using torque to yield fasteners in many applications to use the bolt stretching to actually help maintain torque over time.