Heli-coil 3591-7CNW438 7/16-20 Unf Locking Insert 304 Ss

Product Description

The HELI-COIL 3591-7CNW438 is a tangless screw-locking helical coil insert designed to create or restore strong, vibration-resistant threaded connections in a host material. Manufactured from Grade 304 stainless steel with a dry film lubricant finish, it accepts a 7/16-20 UNF fastener thread and provides a 1D length-to-diameter ratio with an overall installed length of 0.438 inches. The locking function is built into the insert coil itself, eliminating the need for separate locking hardware. Maximum locking torque is rated at 100 inch-pounds, and minimum break-away torque is 14 inch-pounds. Machinists, maintenance technicians, and MRO professionals install these inserts to reinforce tapped holes in aluminum, cast iron, and similar host materials.

This insert is suited for aerospace, automotive, industrial, and general mechanical applications where thread integrity under vibration or repeated assembly cycles is required. The tangless design eliminates the installation and removal steps associated with tanged inserts, reducing assembly time and the risk of tang debris in the host bore. The dry film lubricant coating aids consistent torque control during fastener installation. Single-insert packaging supports repair and low-volume production use; minimum order quantity is 25 pieces.

Key Features

• 7/16-20 UNF thread size with 1D length-to-diameter ratio and 0.438-inch overall length
• Grade 304 stainless steel construction for corrosion resistance in demanding environments
• Tangless design eliminates tang break-off steps and reduces debris risk in blind holes
• Dry film lubricant finish supports consistent installation torque and reduces galling
• Maximum locking torque of 100 inch-pounds with minimum break-away torque of 14 inch-pounds
• 6-5/8 free coils; outside diameter range of 0.524 to 0.549 inches for proper host hole fit

Compatibility

Designed as a screw-locking replacement or thread-repair insert for tapped holes requiring a 7/16-20 UNF internal thread with a 1D insert length. Verify host material tap size per HELI-COIL installation specifications before use.

Installation Notes

Installation requires a HELI-COIL-specified tap to prepare the host hole to the correct oversize diameter before insert placement. A compatible tangless installation tool should be used to drive and seat the insert without damaging the coil or host material. Power down or de-energize any assembly before performing thread repair on in-service components. Refer to applicable torque specifications for the fastener being used after insert installation is complete.