Heli-Coil inserts are precision formed coils of extremely hard, diamond shaped 304 stainless steel. When installed into an STI tapped hole, they provide permanent conventional 60° internal screw threads. This assembled insert accommodates any standard bolt or screw as per MIL-S-7742 and AS8879 (UNJ controlled root radius).
Heli-Coil inserts are larger in diameter before installation than the tapped hole. During installation the inserting tool applies torque to the tang reducing the diameter of the leading coil permitting it to enter the tapped thread. After installation, each high tensile coil of the insert expands outward with a spring-like action permanently anchoring the insert.
All Heli-Coil Inch Screw-Lock inserts are supplied with a red coloring in accordance with NASM21209.