Helical Insert
Threaded Inserts · Heli-Coil (brand) · wire thread insert · screw thread insert
Definition: A helical insert (Heli-Coil is the leading brand) is a coiled stainless-steel wire that forms a durable, wear-resistant internal thread — used to repair stripped threads or reinforce soft materials.
Anatomy
■ Head■ Shank■ Threads■ Point
Governing standards: ASME B18.29.1
Common Sizes
| Inch | Metric | Head width | Head height |
|---|---|---|---|
| #8-32 | M4 | 0.224 drill | STI tap |
| 1/4-20 | M6 | 0.249 drill | STI tap |
| 3/8-16 | M10 | 0.390 drill | STI tap |
Representative sizes. Full dimensional data lives in the standards listed below.
Grades & Strength
| Grade | Material | Tensile (psi) | Marking |
|---|---|---|---|
| 304 stainless | 304 stainless wire | — | Standard |
| Phosphor bronze | phosphor bronze | — | Non-magnetic |
| Inconel | nickel alloy | — | High temperature |
Materials
- 304 stainless steel
- Phosphor bronze
- Inconel (high-temp)
Pros & Cons
Pros
- Restores a stripped hole to like-new strength
- Improves thread wear resistance
- Small, standard drill + STI tap
Cons
- Requires an STI (special) tap
- Insert can unwind if improperly installed
- Not ideal for very soft parent material
Typical Uses
- Stripped-thread repair
- Reinforcing aluminum and magnesium threads
- Engine and transmission cases
- High-wear threaded holes
Alternatives & Related
- Key-Locking Insert — Solid bushing, stronger in soft materials
- Rivet Nut — Where you need a thread in thin sheet
Where to Buy
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FAQ
How do you install a helicoil?
Drill to the STI drill size, tap with the matching STI tap, then wind the insert in with the installation tool until it is 1/4 to 1/2 turn below the surface, and break off the tang.
Heli-Coil vs Keensert?
A helical insert is compact and repairs standard threads; a key-locking insert is a solid bushing that resists much higher loads in soft parent material but needs a larger hole.