Design Guidelines

Heli-Coil inserts provide a positive means for protecting and strengthening tapped threads in any material. Commonly used in OEM design, the unique design features of the insert offer many benefits.

Assembly Strength

Heli-Coil offers maximum design flexibility while adhering to conservative engineering practice, allowing use of Heli-Coil inserts in virtually any application.

Five lengths of inserts are available. In the Heli-Coil catalog (HC2000), the lengths are listed as multiples of the nominal thread diameter of the screw; 1, 1-1/2, 2, 2-1/2,  and 3.

This choice of insert length balances the bolt tensile strength against the shear strength of the parent material. This allows for the design of assemblies where the bolt will fail before the parent material.

Assembly strength is a function of shear area and the shear strength of both the bolt and parent material.

For detailed charts on specific load values, Heli-Coil Technical Bulletin 68-2 (inch) covers the complete range of sizes, parent materials and bolt strengths.

Corrosion Protection

The effect of corrosion on threaded assemblies is dependent on many factors:

• Environment
• Types of metals used
• Sealing mechanisms 
• Length of service

The following recommendations apply for minimizing the effects of corrosion on Heli-Coil stainless steel insert assemblies at operating temperatures less than 800°F, using carbon steel or alloy steel bolts.

The following definitions apply:

• Normal Service: Natural atmosphere environment with the screw always assembled in the insert
• Severe Service: Mildly contaminated atmospheric conditions involving moisture, occasional exposure to salty air or sea spray, and the screw may be left out of the insert for extended periods of time
• Extremely Severe Service: Assembly is exposed to salt water, corrosive atmosphere, and/or the screw is out of the assembly frequently allowing a blind hole to trap water