3591-4CN250 - Helicoil ® Threaded Insert by Stanley ® Engineered Fastening

The Heli-Coil® 3591-4CN250 is a tangless, screw-locking wire thread insert precision-manufactured from 304 stainless steel. Designed to establish permanent, high-strength 1/4-28 UNF fine internal threads in low-density parent materials like aluminum and magnesium, its tangless design completely eliminates tang break-off and retrieval steps, accelerating assembly workflows while eliminating foreign object debris (FOD) hazards. Internal resilient locking coils exert continuous radial pressure on the mating male fastener to resist rotational loosening caused by severe shock and vibration without requiring external lock washers or safety wire.

Tangless Wire Construction eliminates tang removal and vacuum retrieval steps, shortening assembly cycles and completely preventing foreign object debris (FOD) hazards.

Screw-Locking Mechanism features straight-segment internal coils that securely grip bolts to prevent vibration-induced loosening without needing lock washers.

304 Stainless Steel Material delivers superior tensile strength, wear resistance, and long-lasting protection against corrosion in precision components.

1/4-28 UNF Fine Threading reinforces soft parent metals and protects fine-pitch tapped holes against wear, stripping, and galling.

1D Nominal Length Ratio optimizes load distribution and thread engagement depth in space-constrained, compact structural joints.