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Common Questions about Threaded Inserts
What is a threaded insert?
A threaded insert is a metal sleeve installed into a host material to provide a strong, durable thread. Inserts are used where the host material is too soft for direct threading — timber, plastic, aluminium — or where threads will see repeated assembly and disassembly. Common types include wire-thread, self-tapping and press-fit inserts.
What is the difference between a Helicoil and a self-tapping insert?
Helicoil-style or wire thread inserts are coiled stainless wire that screws into a tapped hole, providing a hardened internal thread. Self-tapping inserts have external cutting threads and screw directly into a drilled hole — they cut their own thread in soft materials like timber, plastic and soft alloy without pre-tapping.
Why would I use a threaded insert?
Common reasons include repairing stripped threads in aluminium engine blocks, gearbox housings or machine castings; strengthening threads in soft materials such as timber, plastic and soft alloy; creating reusable threads in housings that see repeated assembly; making threads in materials too soft to hold load reliably without an insert.
Are threaded inserts permanent?
Wire thread inserts are designed to be permanent — once installed they grip the host thread tightly and do not back out under normal load. Self-tapping inserts are permanent in soft materials. Specialised inserts with retention features, such as Keenserts, use locking keys for high-vibration permanent installs in critical applications and structural joints.
What materials are threaded inserts available in?
Stainless steel is the workshop standard for wire thread inserts — strong, corrosion-resistant and suiting most applications. Brass and aluminium self-tapping inserts serve electrical, decorative and lightweight assembly work. AIMS stocks Recoil and other branded threaded inserts across metric and imperial sizes for workshop, automotive and industrial use.
Threaded Insert Selection — Quick Reference
Threaded inserts repair stripped/damaged threads, reinforce threads in soft materials (Al/plastic), and create durable threads for repeated assembly. Selection turns on substrate (Al/steel/plastic), load (light/heavy), and whether removability matters.
| Insert Type | Best For | Brand |
|---|---|---|
| Wire Thread Insert — Tang | General-purpose thread repair in aluminium + soft metals | Recoil (workshop standard) |
| Wire Thread Insert — Tangless | Aerospace + critical engineering — no tang break-off contamination | Recoil tangless |
| Key-Locking Insert | HEAVY-load applications — solid bushing locked by keys driven into base material | EZ Lok, KLI |
| Threaded Bushing (Solid) | Repeated assembly + disassembly — bolts won't strip the insert | Time-Sert, KLI |
| Self-Tapping Insert | Soft material (plastics, soft Al) — cuts its own thread on install | EZ Lok |
| Press-In Insert (Knurled) | Thermoplastics — pressed/heat-staked into moulded hole | Tappex, EZ Lok |
| Helical Coil Insert | Same as wire insert — alternative branding | Helicoil (legacy) |
| Time-Sert (Solid Bushing) | HEAD BOLT + CRITICAL LOAD repairs — strongest single-use solid insert | Time-Sert |
Critical: Match insert thread (internal) to bolt + drill/tap (external) to substrate. Recoil + Time-Sert kits include matched drill + tap + installation tool for each size. Wire inserts give thread strength in aluminium often stronger than steel original (load distribution along the helix). For thread extraction first, see extraction tools. Brands: Recoil, EZ Lok, KLI. Companion: threading, taps, cobalt drill bits.
Threaded Inserts for Thread Repair and Reinforcement
Threaded inserts repair stripped, damaged, or worn threaded holes, create strong threaded connections in soft materials such as aluminium and plastics, and reinforce threads in components subject to repeated assembly and heavy loading. The insert is installed into a prepared oversize hole where it creates a new correctly sized internal thread that is typically stronger than the original base material thread. AIMS stocks threaded inserts in a comprehensive range of metric and imperial sizes across the major insert types for engineering, maintenance, and production applications across Australian industry.
Wire Thread Inserts — Recoil
Wire thread inserts — supplied under the Recoil brand — are coil-wound stainless steel inserts that provide a new internal thread when installed in a tapped oversize hole. They are the most widely used thread repair method in engineering workshops due to their comprehensive size range, the strength of the repaired thread in aluminium and other soft metals, and the availability of installation kits containing drill, tap, and insertion tool for each size. Tang-drive inserts require a tang break-off tool after installation. Tangless inserts — the preferred type in aerospace and critical engineering applications — eliminate this step and remove the risk of broken tang fragments contaminating sealed bores or precision components.
Key-Locking Inserts
Key-locking inserts are solid steel or stainless steel inserts with external coarse threads and internal machine thread, locked in place by keys driven into slots on the insert body after installation. They provide higher pull-out resistance than wire thread inserts and are preferred in applications subject to heavy axial loads, vibration that could unscrew a threaded-in insert, or where permanent locking against rotation is required. Key-locking inserts are widely used in aerospace, heavy engineering, and defence equipment applications where the integrity of the threaded joint is critical to structural safety.
Press-In and Moulded Inserts for Plastics
Press-in inserts for plastics and soft metals use knurled or serrated external features to grip the host material when pressed or driven into a pre-drilled hole. Heat-set inserts for thermoplastics use a soldering iron or heat installation tool to soften the surrounding plastic during insertion, producing a strong flush installation as the material cools and solidifies around the insert's external features. These are widely used in injection-moulded housings, enclosures, and structural plastic assemblies where standard tapped threads in the base plastic would strip under normal fastener clamping forces.
For insert sizing, thread repair solutions, or installation kit supply, contact our team.
When to use a threaded insert — Australian application cases
Threaded inserts solve one of the most common failure modes in Australian fabrication and field maintenance: the host material is too soft to hold a thread, or the joint will see repeated assembly and disassembly that strips a tapped thread over time. Aluminium engine castings, plastic enclosures, magnesium machinery housings, timber structural elements, and soft alloys all benefit from the insert solution. The Australian industries that drive most insert demand are aerospace and defence MRO (where thread repair on aluminium engine and gearbox housings is constant), heavy vehicle and earthmoving repair (where stripped threads on aluminium hubs, brackets and casings stop a machine), marine fabrication (where stainless inserts in aluminium and timber resist galvanic and saltwater corrosion), electronics and enclosure manufacturing (where plastic housings need repeated assembly access points), and general engineering workshops doing thread repair on customer machinery.
The buyer decision splits into two categories. New-build inserts go into a designed joint where the host material isn't suitable for direct tapping — choose insert type for the host material and the expected number of assembly cycles. Repair inserts restore a stripped existing thread — choose the kit that matches the original thread size and the available material around the damage. Both categories use the same insert technology but the installation workflow and tap drill sizing differ.
Insert types AIMS stocks and which to choose
Wire thread inserts (Recoil and Helicoil-pattern) are the most common general-purpose choice. They're coiled stainless steel wire with a diamond-shaped cross-section that springs into a tapped insert thread in the host material. They distribute clamping load across multiple threads in the host, work in aluminium, magnesium, cast iron and timber, and are removable with a removal tool. Recoil's Free-Running, Screw-Lock (with prevailing-torque lock for vibration resistance) and Tangless variants cover the practical range.
Key-locking inserts (Keensert, Heli-Coil Kee-Lok) are solid threaded sleeves with locking keys driven into the host material to prevent the insert rotating in service. They're the heavy-duty choice for high-vibration applications and softer hosts (aluminium engine blocks, transmission housings) where a wire insert might rotate under repeated assembly torque. The trade-off is larger installation footprint and a one-way installation — once the locking keys are driven, removing the insert means destroying it.
Self-tapping inserts (E-Z Lok and similar) thread directly into a pilot drill hole in the host. The external thread is coarse and self-cutting; the internal thread is the working size. They're the fastest installation method and suit field repair where speed matters more than ultimate strength.
Press-fit and ultrasonic inserts for plastic install into a moulded boss without threading the host. They're the production-engineering choice for injection-moulded enclosures, automotive trim and electronics housings where the host plastic can't be tapped reliably.
Thread repair workflow — restore a stripped thread without scrapping the part
The standard thread repair workflow with a Recoil-style kit: identify the stripped thread size (e.g. M10×1.5), select the kit that matches that thread, drill out the damaged thread to the kit's specified tap drill size, tap the new hole with the STI (Screw Thread Insert) tap supplied in the kit, install the wire insert with the installation tool, and snap off the installation tang. The restored thread is now stronger than the original tapped thread in the host material because the insert distributes load across multiple turns and the stainless wire is harder than the host. The same workflow scales from M3 hobby work through to M48 heavy-engineering thread repair.
Cross-link to the wider AIMS thread repair ecosystem: pair with the Recoil 3-generation cross-reference guide for the complete RC code mapping across legacy and current Recoil kits. For damaged taps that need extraction before repair, see tap extractors and the broken tap removal guide. For stripped male threads (bolts, studs) rather than female (tapped) threads, see stripped thread repair guide.
Australian standards that apply to threaded inserts
Wire thread inserts are covered internationally by NASM 8846 (formerly MIL-I-8846) — the US military / aerospace specification that defines insert dimensions, materials and quality. Most reputable inserts including the Recoil range are manufactured to NASM 8846 even where the application isn't aerospace, because the spec sets the dimensional tolerances that ensure interchangeability with the standard STI taps. For the parent thread (the bolt that screws into the insert), the standard metric thread tolerances per ISO 965 apply unchanged — the insert presents a normal female thread to the male fastener. AS 1110 (ISO metric precision hexagon bolts) and AS 1112 (ISO metric hexagon nuts) cover the fasteners that go into the inserts. For the parent material side, the host material standard applies — AS/NZS 1664 (aluminium structures) or AS/NZS 3990 (mechanical equipment - steelwork) depending on the application.
Insert sizing — what to specify when ordering
For new-build applications: specify the internal thread size (the working bolt thread, e.g. M10×1.5), the insert length (typically 1× to 2× the bolt diameter depending on host material — softer hosts need longer inserts), the insert type (free-running, screw-lock for vibration, key-locking for heavy duty), the material (stainless 304 for general, stainless 316 for marine and aggressive chemistry, Inconel for high-temperature aerospace).
For repair applications: specify the damaged thread size, confirm the host material allows the slightly larger tap drill required for the insert, and consider whether the original stud or bolt can be reused or whether you need a fresh fastener too. AIMS supplies complete Recoil thread repair kits that bundle the inserts, the STI tap, the installation tool and the tang break-off tool in one package.
Threaded inserts — common questions
What's the difference between a Recoil insert and a Helicoil insert?
Mechanically they're the same technology — both are diamond-section coiled stainless steel wire inserts installed in an STI-tapped hole in the host material. Helicoil is the original brand name (now owned by Stanley Engineered Fastening); Recoil is a competing brand manufactured in Australia and supplied globally. They're dimensionally interchangeable and use the same STI tap dimensions, so a Recoil insert installs into a Helicoil-prepared hole and vice versa. AIMS stocks Recoil for the Australian supply chain advantage — local stock, local parts, and the complete cross-reference between legacy and current Recoil product codes is documented in our cross-reference guide.
Are wire inserts stronger than the original thread in aluminium?
Yes, typically substantially stronger. The wire insert is stainless steel, which is harder than the aluminium host. Failure mode shifts from thread shear in the aluminium (the original failure mode) to bolt failure or bearing failure of the host material around the insert. This is why aerospace and high-vibration applications routinely specify inserts even in new-build parts where direct tapping would be possible — the joint is more reliable.
Can a wire insert be re-used after the bolt is removed?
Free-running wire inserts can be re-used through many assembly cycles — the host thread (in the insert) doesn't wear because the bolt engages the hardened stainless insert, not the soft host. Screw-lock inserts (with the prevailing-torque feature) lose locking force progressively with each assembly cycle and should be replaced after 5–15 cycles depending on the application. Key-locking inserts are not re-usable once removed.
Do I need a special tap to install a wire insert?
Yes. Wire inserts require an STI (Screw Thread Insert) tap, which cuts a slightly oversized thread to accept the insert. The STI tap is specific to the insert size — an STI tap for M10 wire insert is a different physical tool from a standard M10 tap. AIMS thread repair kits include the correct STI tap; for production volumes where the tap wears, order replacement STI taps separately.
What happens if I cross-thread a bolt into a wire insert?
Less than you'd think. The wire insert is supported by the host material around it, so the failure usually shows as bolt thread damage rather than insert damage. Run a thread chaser through the insert and try a fresh bolt — most cross-thread incidents recover.
Can I install a wire insert without specialist tools?
Field repair kits include all the tools needed (STI tap, installation tool, tang break-off tool). For one-off repairs an inexpensive field kit pays for itself on the first job. Production installations use power tools — pneumatic insert installers speed the workflow by an order of magnitude for OEM and high-volume aerospace work.
For thread repair kit sizing, application-specific recommendations or bulk supply pricing, contact our team.