Technical information

What are wire thread inserts?

Sometimes referred to by the brand names of Helicoil® or Recoil®, helically-coiled wire thread inserts are a thread strengthening fastening device used to create high strength threads in softer core materials. The high performance internal thread provided by our wire inserts is far stronger than most parent materials, and is also heat, corrosion, and wear resistant too.

We manufacture inserts in free running and screw locking type, and produce sizes in a range of thread forms such as Metric, UNC, UNF, BSW, BSF, BSP, BA, NPT, and BSC.

Our standard inserts are made from aircraft quality wire that is cold worked in accordance with SAE AS 7245. These inserts:

• Have a high degree of toughness and hardness
• Have excellent corrosion resistance
• Have tensile strength up to 1400 N/mm²
• Have a hardness of RC 43-50
• Can withstand a temperature range of -200°C to +325°C without detriment to its properties
• Can withstand temperature surges up to 425°C.

Free running inserts

Larger in diameter than the tapped hole, the insert is compressed during installation to ensure maximum surface contact between the flanks of the wire insert and tapped threads. Once fitted, the action of the radial pressure between the insert’s coils and flanks of the tapped hole holds them in place securely.

The flexibility of our inserts enhances load bearing capacity by deflecting the residual forces into a helical direction, which is dispersed into the wall of the tapped hole.

Screw locking inserts

Our screw locking inserts have all of the advantages of a free running type plus the additional benefit of prevailing locking torque, which makes them a valuable and reliable choice for use in applications subject to cyclic vibration or impact.

The locking torque is achieved by the action of a polygonal grip coil in the insert that exerts radial pressure on the male thread, with each grip coil consisting of a number of tangential locking chords that protrude inside the minor diameter of the normal free running coils. As the male thread passes through these grip coils, the locking flats are displaced, thereby exerting radial pressure and prevailing locking torque on the male thread.

On removal of the male thread, the locking coil relaxes to its original form, allowing for repeated assembly whilst retaining a measurable level of prevailing torque.

Wire thread insert installation method

There are six basic stages for installing wire thread inserts:

1. Depending upon your application, either drill a new hole or drill out the damaged thread.
2. Tap thread in the hole using a wire insert tap. A standard tap will not provide the correct thread.
3. Check the tapped hole using a wire insert gauge. This is an important step, as an incorrectly tapped hole will cause difficulties when installing the wire insert, and it may even make it impossible to install the insert altogether.
4. Use your tool of choice to install the insert into the hole. Wind the insert until it is positioned approximately 1/4 to 1/2 a pitch below the surface. Avoid using downward pressure during installation as this may cause the insert to jump threads.
5. Use a tang break tool or a plain pin punch to break off the tang. Remove the loose tang from the hole.
6. Check the installed insert using a thread plug gauge.

Struggling to install inserts?

There are a number of reasons as to why you may be having some trouble with installing your wire inserts. Often, it is a problem with the tapped hole or tooling. Please refer to the table below for solutions to some of the most common problems: