Screw the convex nut (tightening nut) onto the target bolt manually.
Use a wrench, torque wrench or other tightening tool to tighten the convex nut to the torque required for the target application. The convex nut has the same nut strength as a standard single nut without using a prevailing torque, so it can be tightened in the normal fashion.
At this point, the convex nut has exactly the same strength as a general-purpose nut.
Place the concave nut (lock nut) on the convex nut and tighten manually until it no longer turns.
Before continuing with a tool, make sure that the gap between the convex nut and concave nut is about one thread pitch. If not, please refrain from using the Hardlock Nut with this bolt. If the gap is narrower than one thread, the nuts will not lock with adequate strength. When reusing a Hardlock Nut, also make sure there is a one thread gap.
Use a torque wrench to tighten the concave nut to the Hardlock recommended torque.
Even if the nuts are tightened correctly, a gap may remain depending on the bolt diameter tolerance. Regardless of whether there is a gap, if tightened correctly as described above, the Hardlock Nut will provide a strong locking effect.