Spiralock® vs. Locking Inserts... FAQ’s

The KFS Tech Group occasionally gets questions concerning the use of Spiralock as a replacement for threaded inserts. Spiralock is a unique, self-locking, internal thread form that has specific application benefits. However, Spiralock is not a means of replacing all of the design features and benefits of helical coil locking inserts.

Spiral lock

Spiralock provides a locking action on the male fastener as long as the assembly clamp load is maintained (i.e. the bolt remains tight). If the assembly loosens, there is no longer any locking action or prevailing torque on the male fastener. However, locking helical coil inserts provide a locking action (prevailing torque) even if the assembly were to lose its clamp load, thus minimizing the possibility of the male fastener coming completely out of the assembly (see diagram below).

The following are additional features of helical coil locking inserts that are not provided by Spiralock:

  1. Stainless steel inserts provide hard (Rc 43-50), reusable threads in lightweight metals like aluminum, that are resistant to wear and stripping. With Spiralock, the thread would be tapped directly into the softer parent material.
  2. Inserts provide an abrupt starting thread that speeds the assembly time of the male fastener, and eliminates cross threading.
  3. Inserts provide stronger assemblies in parent materials than tapped threads alone. This is because inserts have a larger major diameter, which increases the shear area in the parent material.
  4. Maximum clamping action and bolt tension are assured with minimum wrench torque because inserts have a smooth (8-16 micro inch) finish.

Other factors to consider before using Spiralock to replace locking inserts:


It is our opinion that locking inserts cannot be replaced by Spiralock for all of the previously discussed reasons. Moreover, if an insert loses its locking action because it has exceeded its design cycle life, it can easily be removed and replaced with another insert.

If you have any questions, please contact us.

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