Armstrong ArmaCoil inserts allow you to protect and strengthen all tapped threads. Armstrong ArmaCoil inserts are mirror-smooth, 
reinforced internal threads of 18-8 stainless steel, or of other materials, with a hardness far in excess of the usual tapped materials. 

The outstanding engineering features of ArmaCoil inserts, long recognised by the leading aircraft, industrial and military equipment 
manufacturers, have ensured their widespread use in these fields. 

Armstrong ArmaCoil inserts are manufactured in a wide range of materials and platings to suit different usage needs, such as high 
temperature applications, corrosion & stress cracking resistance, salt water applications, electrical conductivity, and non-magnetism. 


Armstrong ArmaCoil Insert Materials

• Stainless steel
• Nitronic 60
• Nimonic 90
• Inconel X750
• Zeron 100
• Phosphor Bronze


Armstrong ArmaCoil Insert Platings

Where corrosion or galling resistance is required, or additional lubrication is needed in high friction applications, surface treatments 
can be added to standard stainless steel ArmaCoil inserts. 

Some of these treatments include:

•Cadmium Plating
•Silver Plating
•Zinc Plating
•Dry Film Lubricated

In latest developments, new treatments such as Cadmium Plate & Olive Drab and ArmaGuard (which prevents galvanic corrosion 
between insert and parent material) have been created to cater to market demand.

Five lengths of Armstrong ArmaCoil inserts for each thread size are available - lengths of 1, 1.5, 2, 2.5 & 3 times the thread diameter 
of the bolt. These different ArmaCoil insert lengths offers the designer the opportunity to balance the tensile strength of the bolt 
material against the shear strength of the parent material. 

ArmaCoil Screw Thread Inserts are available in:

•Metric (Coarse & Fine)
•Whitworth (BSW, BSF, BSPF, BA)
•Unified Thread (UNC & UNF)
•Spark Plug 

Armstrong ArmaCoil TwinCoils are used to salvage wire thread insert holes that have become worn or stripped, 
as well as in the correction of out-of-position holes and tapped holes that are gauged to be oversized. 

The ArmaCoil TwinCoil system consists of two ArmaCoil inserts. An Outer ArmaCoil TwinCoil is installed into an 
oversize tapped hole, which has an Inner ArmaCoil TwinCoil fitted inside to give a standard female thread.


The Outer TwinCoil insert is installed into the TwinCoil tapped hole (larger than a conventional wire thread 
insert tapped hole) and is the same nominal length as the original thread. The Outer TwinCoil is always a free 
running insert while the Inner TwinCoil insert can be either free running or screw lock, depending on the 
application.

As the Inner TwinCoil insert must be supported by the Outer TwinCoil insert, its length is ONE COIL shorter than 
the Outer TwinCoil insert. This allows the Inner TwinCoil insert to be installed below the end of the Outer 
TwinCoil insert at each end.

Thread lengths less than 1.5 times the nominal diameter are usually not available. This is due to reduced 
thread engagement affecting the assembled strength to a potentially un-acceptable level.

Armstrong ArmaCoil Free Running Inserts 

Armstrong ArmaCoil free running inserts are manufactured from high tensile stainless steel wire, formed 
into a diamond section, to exacting dimensional standards.  When installed, the ArmaCoil insert provides 
a precision female thread of high surface finish and strength. 

Armstrong ArmaCoil Screw Locking Inserts 

In addition to all the characteristics of free running inserts, the Armstrong ArmaCoil Locking insert has 
one or more of its intermediate coils deformed polygonally. This creates strong resilient pressure onto 
the thread flanks of the bolt as it passes through the ArmaCoil Locking insert. This in-built prevailing 
torque of the grip coil positively locks the inserted bolt, preventing it from loosening under vibrations 
or impact. Screws can be inserted by hand up to the grip coil, after which some mechanical means 
must be employed to overcome the locking medium. 

ArmaCoil Locking inserts are coloured red for identification purposes only, to distinguish them from 
free running inserts.