CoilThread Inserts are helically-coiled fastening devices that provide permanent, wear-resistant screw threads that exceed the strength of most parent materials. CoilThread Inserts are made of cold-rolled 304 stainless steel wire (AS7245), work-hardened to a tensile strength above 200,000 psi, and a hardness of Rc 43-50. The finished surface (32 microinches) is exceedingly smooth, virtually eliminating friction-induced thread erosion.

KATO CoilThread inserts are available in Unified Coarse (UNC), Unified Fine (UNF) and Metric thread sizes. CoilThread Inserts can also be made of Nitronic 60®, Nimonic 90®, Phosphor Bronze, and more. See KATOpedia for more Insert Materials.

Why use CoilThread Inserts?

CoilThread Inserts provide design and manufacturing flexibility.


The image above depicts weight and space
savings provided by utilization of CoilThread Inserts.
All three samples have the same internal thread, and as you
can see CoilThread Inserts require the smallest boss diameter.

KATO CoilThread Inserts are based on a continuous helically-coiled open pitch design using a diamond shaped wire. The material thickness requirement is less than the material required by solid inserts or thin wall inserts that support an internal thread of the same nominal size. The diamond-shaped wire design allows the inserts to engage the threads in the parent material and at the same time accept a male fastener. Thus, they do not need a thick wall structure to support the internal and external threads.

The resilient characteristics of each coil in a CoilThread Insert allows it to adjust independently to secure the maximum surface contact with individual threads in the parent material. As a result, loads are distributed more evenly than solid threads. Stress and fatigue concentrations are reduced to maximize thread strength and increase the reliability and life of the fastening system. CoilThread Inserts are designed to be installed in reduced-sized bosses or flanges and within constricted areas, thus saving space and weight while providing high strength. A boss radius equal to the nominal bolt diameter is usually sufficient.

Precision engineering, exacting manufacturing standards, and stringent quality control procedures are utilized during entire manufacturing process to assure a high quality product that meets or exceeds all applicable military and aerospace standards. KATO CoilThread Inserts have been put through rigorous torque, tension, and vibration tests as well as comprehensive dimensional inspections and metallurgical analysis in attaining their MIL-SPEC qualifications. CoilThread Inserts have been thoroughly tested by an independent testing laboratory and are certified to conform to NASM8846.

When installed into STI tapped holes (per NASM33537 for unified and MA1567 for metric), CoilThread inserts provide a finish thread meeting the requirement of FED-STD-H28. Assembled CoilThread insert will also accommodated UNJ (MIL-S-7742 and AS8879) male threaded fasteners. For additional information on applicable military and aerospace standards please refer to the MA/MS/NAS Specs.

Tangless CoilThread vs CoilThread (Tanged)

KATO Tangless CoilThread Inserts are identical, in form, fit, and function to the conventional Tanged inserts (CoilThread, Helicoil, Recoil).
In fact, Tangless CoilThread Inserts are identical to Tanged inserts in every way expect for their method of installation and removal, and they have the exact same procurement specification (NASM8846 for unified sizes and MA1565 for metric sizes).


Tangless CoilThread

  • FOD-Free Design: No tangs to break off, retrieve or lose.
  • Approved for use on military programs by NASM8846, NAS1130, and NA0276.
  • Cost Reduction: Significantly decreases installation and inspection time.
  • Bi-Directional design eliminates insert orientation requirements.
  • Quick, non-destructive removal prevents damage to the parent material.

CoilThread (Tanged)

  • Lower pricing than competitive inserts.
  • Complete range of  unified and metric sizes, locking and non-locking, bulk and strip-feed.
  • Meets or exceeds all applicable military, aerospace, and commercial standards. Full traceability.