MIL-I-8846
Helical Coil Inserts
Mumbai · India
Why a Wire Insert, Not a Bigger Bolt
A helical coil insert solves a problem that has nothing to do with the fastener itself and everything to do with the material it threads into. Aluminum and magnesium castings and machined parts are common throughout aerospace and precision equipment specifically because they’re light — but a thread cut directly into aluminum or magnesium is genuinely much weaker and more wear-prone than a thread cut into steel, and a bolt that’s repeatedly removed and reinstalled into a soft aluminum tapped hole will eventually strip that thread regardless of how good the bolt is.
MIL-I-8846 inserts solve this by lining the tapped hole with a precision-wound stainless steel wire coil that presents a hard, wear-resistant steel thread to the incoming bolt while still being securely wound into the original soft-metal tapped hole. The bolt effectively never touches the aluminum thread at all — it engages the steel coil instead, which is dramatically more resistant to wear, galling, and thread damage from repeated assembly and disassembly than the aluminum ever could be on its own.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our helical coil insert range is manufactured across free-running and screw-locking types, verified by dimensional and torque testing under our ISO 9001:2015 quality system.
Where This Specification Genuinely Applies
Dramatic Thread Strength Gain
Presents a hardened steel thread inside a soft-metal hole, multiplying effective thread strength and wear life.
Repairs Stripped Threads
Can restore a stripped or damaged tapped hole to full original thread strength, or beyond.
Reduces Galling Risk
Stainless steel coil thread reduces the galling risk that similar-metal bolt-into-aluminum threading carries.
Verified Coil Tension & Fit
Batch testing confirms genuine coil tension and thread engagement, not just correct nominal size.
Free-Running vs Screw-Locking Inserts
Free-Running Helical Coil Insert
Standard coil form with no built-in locking feature, for general thread reinforcement or repair applications.
Screw-Locking Helical Coil Insert
Includes a deformed coil section that grips the bolt thread, adding prevailing torque locking to resist vibration loosening.
Tang-Break-Off Design
Installation tang snaps off cleanly after the coil is wound into place, leaving a clean finished thread.
Insert Type Selection Guide
The right insert type depends on whether the joint needs vibration-resistant locking or simple thread reinforcement. This table is the quick reference we use with buyers before quoting.
| Requirement | Correct Type | Key Function |
|---|---|---|
| General Thread Reinforcement or Repair | Free-Running Insert | Hardened thread, no locking feature |
| Vibration-Resistant Locking Joint | Screw-Locking Insert | Adds prevailing torque via deformed coil section |
| Restoring a Stripped Tapped Hole | Free-Running (Oversize) | Restores original bolt size, full thread strength |
MIL-I-8846 Specification Details
Materials We Manufacture In
- Stainless Steel Wire 300 Series (18-8)
- Phosphor Bronze Non-Magnetic Applications
- Finish Passivated / Plain
- Coating Available on Request
How Helical Coil Inserts Are Made
- Process Precision Wire Winding
- Cross-Section Diamond Wire Profile
- Testing Coil Tension / Torque
- Quality Batch Sampled
Available Dimensions
- Nominal Size #2 – 1″ (Inch Series)
- Metric Equivalent Available to Drawing
- Length 1D / 1.5D / 2D / 2.5D / 3D
- Type Free-Running / Screw-Locking
Application Areas
Wherever a bolt threads repeatedly into aluminum, magnesium, or other soft base material.
Aircraft Structural Assembly
thread reinforcement
Engine Casings & Housings
housing thread reinforcement
Automotive Casting Assembly
casting thread reinforcement
Precision Machinery Housings
disassembly points
Government & Defense Equipment
thread reinforcement needs
Marine & Naval Equipment
reinforcement in light alloys
Electronics Enclosure Manufacturing
thread durability
General Soft-Metal Thread Repair
hardened thread reinforcement
Standard Export Documentation
Prepared as standard practice for every MIL-I-8846 thread insert shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification for every lot.
Coil Tension & Torque Test Records
Batch-level testing confirming genuine coil tension and installed thread engagement.
Certificate of Conformance
Confirms the shipment matches the purchase order type/size specification in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
NABL Accredited Test Reports
Independent mechanical and dimensional testing available on request for critical applications.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
MIL-N-25027 Self-Locking Nuts
Our companion aerospace self-locking nut specification, often used alongside thread inserts.
View MIL-N-25027 →FF-N-836 Hex Nuts
Our commercial hex nut range for general-purpose, non-aerospace bolted joints.
View FF-N-836 →Titanium Grade 5 Fasteners
Our aerospace-grade titanium fastener range, often paired with helical coil inserts.
View Titanium Gr5 Fasteners →Fasteners Manufacturer & Exporter to the USA
Our broader capability manufacturing to ASTM/ASME and US federal/military standards.
View USA Export Guide →Need a Stronger Thread
in Aluminum or Magnesium?
Tell us your base material, bolt size, and whether locking is needed — we’ll confirm the right insert type and quote with full documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in