Part Number: MS21209, NAMS21209
Function : Insert, Screw Thread, Coare and Fine, Screw Locking, Helical Coil, Cres
Manufacturer: AEROSPACE INDUSTRIES, National Areospace Standard
The MS21209 is screw thread coil.
Heli-Coil inserts are precision formed screw thread coils worked into a diamond shape. The resultant surface finish is a mirror-like 8-16 micro inches. This wire is then wound into a spiral coil which when installed into Heli-Coil tapped holes, provides permanent conventional 60º internal screw threads. This assembled insert accommodates any standard bolt or screw (MIL-S-7742) and MIL-S-8879 (UNJ controlled radius root) male threaded members. (See page 8 for material availability.)
Reference site : https://helicoil.in/helicoil.htm