Heli-coil A1191-4EN250 1/4-28 Unf Free Running Insert

Product Description

The HELI-COIL A1191-4EN250 is a free running wire thread insert designed to create strong, wear-resistant internal threads in parent materials that are softer or more prone to thread damage than the fastener itself. This tanged, stainless steel coil insert measures 0.25 inches in overall length and is manufactured to a 1/4-28 UNF thread specification with a 1D length-to-diameter ratio. It installs into a pre-drilled and tapped hole using a standard HELI-COIL installation tool. Maintenance technicians, machinists, and field service pros use these inserts to repair stripped threads or reinforce new assemblies across industrial, aerospace, and mechanical applications.

This insert is suited for thread repair and reinforcement in a wide range of applications including automotive assemblies, machinery housings, aluminum castings, and fabricated components where a 1/4-28 UNF threaded connection is required. The tanged design allows for positive engagement during installation, and the tang is removed after the insert is seated. This single-insert package is appropriate for low-volume repair work or prototype applications where only one fastener location requires treatment.

Key Features

• 1/4-28 UNF thread size for standard unified fine thread applications
• 0.25 inch overall length with a 1D length-to-diameter ratio for shallow-hole installations
• Tanged style for controlled installation using a standard HELI-COIL driver tool
• Stainless steel construction provides corrosion resistance and durability in the installed thread
• 5 free coils deliver consistent spring action and thread engagement

Compatibility

Designed as an OEM-style thread repair and reinforcement insert for any parent material tapped to accept a 1/4-28 UNF HELI-COIL insert. Requires a matching HELI-COIL tap and installation tool for proper fitment.

Installation Notes

Installation requires a HELI-COIL-specified insert tap to prepare the hole to the correct minor diameter before the insert is driven in. Use the appropriate HELI-COIL installation tool sized for 1/4-28 inserts to seat the coil flush with or slightly below the parent material surface. After seating, break off the tang using a tang break-off tool or a sharp punch applied to the notch at the bottom of the insert. Always de-energize or de-pressurize the assembly before performing thread repair work on live systems.