Heli-coil A1191-4EN375 Free Running Insert 1/4-28 Unf

Product Description

The HELI-COIL A1191-4EN375 is a free running helical wire thread insert designed to provide a strong, wear-resistant internal thread in parent materials that require thread repair or reinforcement. The insert measures 0.375 inches overall length with a 1/4-28 UNF thread size and is manufactured from stainless steel for corrosion resistance in demanding service environments. At a 1-1/2D length-to-diameter ratio and featuring 8-1/4 free coils, it delivers reliable thread engagement in metal components. The tanged design aids installation and is compatible with standard HELI-COIL installation tooling. Licensed machinists, maintenance technicians, and field mechanics install these inserts during thread repair or precision assembly operations.

This insert is suited for applications where original or stripped internal threads need to be restored to full strength or where a harder thread form is needed in softer base materials. It is commonly used in aerospace, automotive, industrial equipment, and general MRO maintenance work. The 1/4-28 UNF thread form is a fine-pitch standard widely found in precision mechanical assemblies. Sold individually, it is available in minimum order quantities as noted by the supplier.

Key Features

• 1/4-28 UNF thread size for fine-pitch precision thread repair and reinforcement
• 0.375 inches overall length with 1-1/2D length-to-diameter ratio for solid thread engagement
• Stainless steel construction provides corrosion resistance and durability
• Tanged design for controlled installation with standard HELI-COIL drive tools
• 8-1/4 free coils deliver consistent coil tension and thread form after installation

Compatibility

Designed as an OEM-style free running insert for 1/4-28 UNF threaded holes requiring thread repair or thread form reinforcement in metallic parent materials.

Installation Notes

Installation requires a proper HELI-COIL tap to prepare the parent hole to the correct insert-accepting thread form before the insert is driven in place using the appropriate installation tool. After installation, the drive tang is broken off using a tang break-off tool or punch. Ensure the parent material is secured and de-energized or depressurized as applicable before beginning thread repair work. Follow applicable shop procedures and torque specifications for the assembly being serviced.