Aluminum and magnesium win on strength-to-weight, so designers keep specifying more of them. The Aluminum Association and Ducker Carlisle project 556 pounds of aluminum per North American light vehicle by 2030. Threads tapped straight into those alloys give up under repeated torque, service cycles, and vibration.
Precision wire thread inserts fix that. They spread clamp load across the full depth of the tapped hole instead of loading the first few threads. Supply matters as much as the part itself. Böllhoff builds more than 20 million fasteners a day across 16 production plants, and the right distribution partner turns that capacity into the correct insert, in the correct bin, on the day your line needs it. Böllhoff’s KOBSERT line, including self-tapping and heat-set inserts for plastics, is covered in our guide to KOBSERT threaded insert specs and sizes.
| Supply Partner | Business Model | Authorized Böllhoff | Best For |
|---|---|---|---|
| Component Solutions Group | Distributor and VMI partner | Yes | OEMs needing design assist and vendor-managed inventory |
| Böllhoff Group | Manufacturer | Yes (original manufacturer) | Direct high-volume enterprise contracts |
| DB Roberts | Distributor | Yes | General electronics manufacturing hardware |
| Fastenal | Distributor | Not published | Local MRO and facility maintenance |
Thread Failure, Galvanic Corrosion, and FOD Risk in Soft-Alloy Assemblies
The first challenge is material shear strength. Aluminum, magnesium, and composites lack the shear strength to hold a steel fastener under high tension. Drive a steel bolt into a tapped aluminum hole and the harder threads cut the softer ones, which produces galling, permanent deformation, and lost clamp load during assembly.
The second challenge is rework economics. Assembly lines need fast, repeatable torque without cross-threading. When a tapped hole strips at final assembly, the part goes off-line for rework or straight to scrap. Repairing a machined casting late in the build destroys the margin on that unit and pushes the delivery date.
The third challenge is cyclic loading. Heavy equipment and aircraft engines generate continuous vibration that walks standard fasteners loose. The vibration beats the friction holding the joint, and the clamp load bleeds off over time. Manufacturers need a threaded joint that protects the parent material, survives repeated service cycles, and holds the fastener against vibration.
The fourth challenge is galvanic corrosion at the insert-to-housing interface. A stainless steel insert sitting in an aluminum or magnesium housing puts two dissimilar metals in contact, and moisture or salt spray turns that contact into a corrosion cell that eats the softer parent metal. Specify a dielectric or zinc-nickel coating on the insert for outdoor, marine, and undercarriage service, and match the coating to the housing alloy rather than defaulting to bare A2 stainless.
The fifth challenge is foreign object debris. Every driving tang that breaks off has to leave the assembly. A tang left loose in a blind hole, a gearbox, or an engine bay is FOD, and aerospace and defense programs treat FOD control as an audit item, not a housekeeping preference. Plan tang retrieval into the work instruction, or specify a tangless insert so there is nothing to recover.
What Is a HELICOIL Insert?
A wire thread insert is a precision-formed coil of cold-rolled wire with a diamond-shaped cross-section. Installed into a specially tapped hole, the inside diameter of the coil forms a precise internal thread that accepts a conventional bolt or screw. The outside diameter presses outward against the base material and locks the insert in place.
That design creates an elastic transition between the fastener and the host metal. The wire flexes slightly, so clamp load spreads across every engaged thread instead of concentrating on the first few. In a plain tapped hole, the top threads take the brunt of the stress and fail first. The insert moves that load down the full engagement length and raises pull-out strength.
Free-Running vs. Screw-Locking Inserts
Engineers pick one of two configurations based on the operating environment. Both use the same tap size and the same installation procedure.
The free-running insert is a smooth, continuous coil top to bottom. It forms a standard thread profile and lets fasteners run in with minimal friction. Specify it for joints that come apart during maintenance, for thread reinforcement, and for basic wear protection in soft metals.
The screw-locking insert carries one or more deformed polygonal coils near the middle. As the bolt passes through, the wire pushes outward and creates prevailing torque against the bolt threads. That friction holds the fastener without thread locker, lock washers, or safety wire. Screw-locking inserts are the right call for repeated service cycles and severe vibration.
Material Options and Specifications
The operating environment dictates the insert material. The correct alloy prevents galvanic corrosion and holds joint integrity under thermal stress.
Type 304 stainless steel, also called A2, is the standard choice for most applications. It gives strong tensile performance and general corrosion resistance. Böllhoff rates 304 wire thread inserts to roughly 600 degrees Fahrenheit long term and 800 degrees Fahrenheit short term. For marine service or harsh chemicals, engineers move to Type 316 stainless, also called A4, for better pitting resistance.
Aerospace and defense assemblies call for specialty alloys. Inconel X-750 holds up in gas turbine and nuclear applications, rated by Böllhoff to about 1,020 degrees Fahrenheit long term and 1,380 degrees Fahrenheit short term. Phosphor bronze suits electrical components that require non-magnetic properties and resists galling well. Nitronic 60 gives strong wear resistance and performs in vacuum environments where standard lubricants evaporate.
Coatings extend those materials further. Dry film lubricants cut installation friction and keep the bolt from seizing inside the insert. Zinc-nickel and dielectric coatings break the galvanic path between a stainless insert and an aluminum housing. Silver plating delivers anti-galling protection in high-heat aerospace work. Cadmium plating still shows up in defense programs that require sacrificial corrosion protection.
HELICOIL Thread Sizes, Drill Charts, and STI Tap Compatibility
Inserts cover nearly every thread pitch in global manufacturing. Metric sizes run from M2 threads in electronics up to M39 threads in heavy construction equipment. Unified inch sizes cover UNC coarse, UNF fine, and UNEF extra-fine standards.
Every size carries a matched drill diameter and a matched STI tap. Work from the published drill chart for the specific insert series, not from a general tap-drill table, because the STI hole runs larger than a standard tapped hole of the same nominal thread. Pulling the drill size off the wrong chart is the most common reason a first article fails gauge inspection.
Specify the engagement length required to hit your target pull-out strength. Engagement length is expressed as a multiple of nominal bolt diameter. A 1.0D insert matches the bolt diameter exactly. Soft materials such as cast aluminum typically need 1.5D or 2.0D so the bolt fails before the threads pull out of the parent metal.
How to Install a HELICOIL: Drill Sizes, Tapping, and Insertion Specs
Installation follows exact machining practice. A poorly tapped hole or wrong insertion depth compromises the joint.
1. Pre-Drilling the Parent Material
Drill with the exact bit size specified for the insert. That size always runs larger than the nominal diameter of the final bolt. Aluminum and plastics take standard drilling speeds. Titanium and hardened steel need specialized bits and slower feed rates to avoid work hardening. Add a standard countersink so the top coil does not catch on entry.
2. Tapping with an STI Tap
The hole requires a Standard Thread Insert (STI) tap. An STI tap cuts the same pitch as the final fastener at a larger diameter to make room for the wire coil. Never substitute a standard tap. Clear the chips, then verify the threads with an STI go/no-go gauge before you install anything.
3. Threading the Insert
The insert threads onto an installation tool by the driving tang at the bottom of the coil. Hold the tool perpendicular to the hole and wind the insert in under light pressure. Drive it until the top coil sits one-quarter to one-half turn below the surface of the parent material. Heavy downward pressure during installation causes cross-threading and skipped coils.
4. Breaking the Tang
Once the insert seats at depth, remove the driving tang so the bolt passes through the full length of the coil. Drop a tang break-off tool into the insert until it rests square against the tang. One sharp hammer strike snaps the tang at the pre-cut notch. Pull the broken tang out of blind holes and account for it on the FOD log so it never interferes with the bolt or the finished assembly.
Tooling Requirements for Production Speed
Installation tooling drives throughput. Prototype work and field repairs run fine on hand tools, which thread the insert manually and rely on visual depth checks.
High-volume OEM lines need pneumatic or electric installers to hold cycle time. Powered tools use a pre-winder cartridge that compresses the insert before it enters the hole, which keeps insertion fast and square. Adjustable depth stops let operators install thousands of inserts to the same spec without stopping for manual inspection. Good Böllhoff installation equipment raises first-pass yield and cuts operator fatigue.
Matching the Right Insert to Your Joint and Environment
Start with the joint. Soft parent metal and frequent disassembly point to free-running inserts at 1.5D or 2.0D. Vibration and repeated service cycles point to screw-locking. Heat, salt exposure, and the housing alloy set the material and the coating. Volume sets the tooling. If the print calls for a solid bushing instead of a coil, a keyed insert such as a Keensert or a self-tapping bushing such as a Time-Sert solves a different problem: maximum wall strength in a thin boss or a badly oversized hole. Wire thread inserts win on weight, cost per hole, and standard tooling across a full size range.
Then judge how the parts actually reach your line. Component Solutions Group pairs engineered fastening with a vendor-managed inventory program, so forecasting, incoming quality, and bin stocking sit with us instead of your buyers. That keeps engineering on product work rather than chasing tracking numbers.
Schedule an engineering consult with our OEM team. We will review your joint designs, confirm drill and STI tap callouts, recommend the right wire thread inserts for the application, and build a stocking program around your production schedule.
Component Solutions Group
Component Solutions Group is an engineered fastening partner and a member of the Bufab Group. We supply C-class components, custom fasteners, and vendor-managed inventory programs to tier-1 manufacturers and OEMs.
CSG is an authorized Böllhoff distributor, so you get authentic wire thread inserts with full traceability. Our engineers work directly with your team to specify the insert, match the installation tooling, and build a stocking program that keeps the line running. For part numbers, size tables, and bulk order guidance, see our fastener portfolio.
Advantages:
- Authorized distributor of authentic Böllhoff inserts and installation tooling.
- Engineering support for joint design, tap selection, and installation method.
- Certified to ISO 9001:2015 and AS9120 B, with ITAR registration.
- Vendor-managed inventory programs that cut total cost of ownership.
Böllhoff Group
The Böllhoff Group manufactures the original HELICOIL product line and owns the trademark. The company supplies automotive, aerospace, and general industrial customers worldwide. Its plants set the technical standards, tolerances, and installation tooling for the entire product family.
Best for massive-volume programs that justify a direct manufacturer contract. Pricing is volume dependent and quoted directly. The standout advantage is primary-source manufacturing and in-house product development.
Advantages:
- Direct access to the company that makes the product.
- Technical data straight from the source, including aerospace material specs.
- Custom manufacturing capability for specialized applications.
Disadvantages:
- Direct minimum order quantities run past what most mid-sized manufacturers need.
- Buying direct gives up the mixed-brand consolidation a distributor VMI program provides.
DB Roberts
DB Roberts is an authorized fastening hardware distributor focused on electronics, sheet metal, and telecommunications. It carries a wide brand mix and ships standardized catalog parts from several distribution centers.
Best for electronics assembly lines and sheet metal fabricators. Pricing follows standard distribution rates through the online catalog. The standout strength is depth in board hardware and standoffs.
Advantages:
- Fast online ordering for standardized hardware.
- Strong selection of electronics-specific fastening elements.
- Authorized status confirms authentic parts.
Disadvantages:
- Thinner support for aerospace and heavy equipment joint engineering.
- Transactional supply model rather than an integrated OEM program.
Fastenal
Fastenal runs local branch locations and industrial vending machines across North America. It stocks hex bolts, safety equipment, and janitorial supplies, which makes it a default for facility maintenance and local pickup.
Best for facility managers and same-day maintenance, repair, and operations needs. Pricing runs higher on low-volume branch pickup. The standout strength is geographic coverage plus vending.
Advantages:
- Branches sit near most industrial parks for immediate pickup.
- One order covers safety gear, tools, and basic fasteners.
- Vending machines simplify consumable tracking.
Disadvantages:
- Generalist product knowledge limits engineering support on critical structural joints.
- Operates as a broad commodity supplier, not a specialized C-parts partner.
Frequently Asked Questions (FAQs)
HELICOIL vs. Keensert vs. Time-Sert: which thread insert should I use?
A HELICOIL is a wire coil that forms a new thread inside an STI-tapped hole, so it is the lightest option and covers the widest size range. A Keensert is a solid bushing with mechanical locking keys driven into the parent metal, which suits high-torque repairs where the coil would spin. A Time-Sert is a solid thin-wall bushing that installs into a stepped hole. Pick the coil for production joints and weight-sensitive parts, and the solid bushings for damaged or oversized holes that need a rigid wall.
How do you install a HELICOIL in aluminum?
Drill the aluminum with the specified drill size, tap the hole with an STI tap, wind the insert in with an installation tool until it sits one-quarter to one-half turn below the surface, then snap off the driving tang with a break-off tool. Remove the tang from blind holes before the bolt goes in.
Where can I find a HELICOIL drill size and STI tap chart?
Drill diameters, STI tap callouts, and engagement lengths are published per insert series in the Böllhoff technical documentation. Match the chart to the exact series and length you are buying, because the STI hole is larger than a standard tapped hole of the same nominal thread. Our engineers confirm the drill size and tap callout against your print before you cut the first hole.
How do you remove a damaged wire insert?
Use an extraction tool. Its blade edges bite into the top coil when you press down. Turning counter-clockwise forces the coil inward and unthreads the insert without damaging the host metal.
Talk to an engineer about your application
CSG stocks and sources engineered fasteners and C-parts for OEMs across aerospace, defense, heavy equipment and industrial manufacturing. Send the drawing, the part number or just the problem, and an applications engineer will come back with options, lead times and pricing.
