How CoilThread Screw Locking Inserts Work:
One of the biggest misconceptions regarding locking type says helically-coiled screw thread inserts is that the insert has a feature which locks it into place in the parent material. This is not the case. Locking inserts apply a locking, or prevailing, torque on the male fastener.
Locking inserts contain one or more coils that have a series of straight segments. Upon entry of the bolt these straight segments are flexed outwardly, creating pressure on the bolt. This pressure is applied between the flanks of the bolt thread so that contact area is maximized.
CoilThread screw locking inserts are manufactured to meet the locking torque requirment specified in NASM8846. NASM8846 requires the inserts to pass a 15 cycle torque test; it is often possible to realize a cycle life far in excess of specification requirements.
For additional information on locking inserts and prevailing torque, please readthese articles in KATOpedia:
Locking Insert FAQ
Locking Torque Differences