Threaded insert types compared: wire, self-tapping, key-locking and heat-set
Every insert in this table creates a durable internal thread that the parent material could not hold on its own — but each one earns that thread a different way, and the installation method is the real decision. This table compares the four insert systems we publish individual specification pages for, using only fields that mean the same thing across the columns. Where a figure is not established by the collected evidence, the cell says so and asks you to confirm it at RFQ; nothing is filled in with an assumption, and no cell implies a type cannot be supplied.
Comparison table
The columns split first by parent material — metal inserts versus plastic-bonded heat-set — and then by which installation step you are able or willing to perform: STI tapping, plain pilot drilling, or key setting.
| Field | Wire (Helical) Insert | Self-Tapping Insert | Key-Locking Insert | Heat-Set Insert |
|---|---|---|---|---|
| Construction & setting principle Differs in kind across the columns: a coil seated in an STI thread, a solid body that cuts its own thread, a solid body pinned by keys, or an insert bonded by softened plastic. | Precision-formed wire wound into a helix — seated into a tapped STI receiving thread with a driving tool; tang broken off after installation | Solid insert with external cutting features — cuts or forms its own thread in the pilot hole during installation | Solid insert with locking keys driven into the parent material after the insert is positioned | Knurled insert pressed in heated — the plastic softens, flows around the external features and locks on cooling |
| Hole preparation | Drill + STI tap — the STI thread is larger than the final thread; a standard tap of the nominal size fails the installation | Drill only — pilot hole per size table (e.g. M6: Ø 8.9–9.4 mm, depth 16 mm); no separate tapping step | Drill + accurate preparation, then insertion and key setting per the manufacturer specification — more careful than simple self-tapping | Prepared hole in plastic — hole size, boss diameter, wall thickness and installation temperature all govern; not the metal-insert pilot-hole logic Conditional — confirm configuration |
| Parent material | Metal — stripped-thread repair and reinforcement in aluminum and other soft metals | Aluminum, soft metals, engineering plastics and repair work | Metal — aluminum and cast components, machine bases, fixture plates | Thermoplastics — 3D-printed parts and injection-moulded components (brass is the default insert material) |
| Anti-rotation under torque How each system resists the insert spinning in its hole — stated only where the collected page states it. | Unverified — the collected page does not state an anti-rotation mechanism for this insert type; confirm at RFQ Unverified — confirm at RFQ | Friction-based — an oversize pilot hole makes the insert spin and lose pull-out strength; the pilot-hole window is the discipline | Positive mechanical lock — keys driven into the parent stop rotation under torque or vibration | Unverified — the collected page does not state a torque rating for the plastic bond; confirm at RFQ Unverified — confirm at RFQ |
| Reference size range Each column quotes its own collected range — the bases differ by column and are not converted. | Unverified — this module's collected guide carries no size ladder; STI tap charts are published separately and confirmed at RFQ Unverified — confirm at RFQ | M3–M12 installation table (OD, length, pilot hole, depth, torque note per size) | Unverified — the collected page does not tabulate a size ladder; confirm sizes at RFQ Unverified — confirm at RFQ | M2.5–M12 mapped to applications — M2.5 small electronics through M10–M12 heavy fixtures and repair work |
| Materials | Stainless steel, carbon steel, brass (per collected guide) | Stainless steel, carbon steel, brass (per collected guide) | Stainless steel, carbon steel, brass (per collected guide) | Brass the plastics default; stainless and carbon-steel variants per the collected material guide |
| Best for | Stripped-thread repair that keeps the original screw size, and wear resistance in frequently assembled metal joints | Skip-the-tapping installations — aluminum plates, cast parts, plastic housings and repair where pre-tapping is the bottleneck | High-load or vibrating points where the insert must not rotate — machine bases, fixture plates, maintenance-heavy machinery | Reusable metal threads in thermoplastics — sensor brackets, printed housings, control panels, actuator covers |
- Verified
- Differs
- Unverified — confirm at RFQ
- Conditional — confirm configuration
How to choose
By the parent material
The first split costs nothing: three of the four systems live in metal and one lives in plastic. Wire, self-tapping and key-locking inserts all reinforce or repair metal — aluminum housings, cast parts, steel plates. The heat-set insert is the thermoplastic specialist — 3D-printed parts and injection-moulded components — where its brass body is bonded by softened plastic rather than by cutting or keys. Putting a heat-set insert in a metal part, or a self-tapping insert in a 3D print, misapplies the system's whole holding mechanism.
By the installation step you can perform
Among the metal inserts, choose by the hole operation. The wire insert needs an STI tap — and only an STI tap; the self-tapping insert needs just a pilot hole drilled inside its per-size window; the key-locking insert needs accurate preparation plus a key-setting operation. Repair work that must keep the original screw size points back to the wire insert; production lines that want to skip tapping point to the self-tapping type.
By the failure mode you fear
If the joint's history includes an insert spinning under torque or vibration, that failure has one specialist answer in this table: the key-locking insert, whose keys are driven into the parent to stop rotation. Where pull-out from thin or weak parents is the risk instead, hole discipline — the pilot-hole window for self-tapping types, the boss and wall parameters for heat-set — matters more than the insert choice, and the surrounding material always governs the joint.
Frequently asked questions
Wire insert or self-tapping insert — how do I decide?
Decide by which operation you can afford and which failure you fear. A wire insert preserves the nominal screw size inside an STI-tapped hole — the conventional stripped-thread repair and the choice for aluminum joints serviced repeatedly — but it needs the STI tap; a standard tap of the nominal size fails the installation. A self-tapping insert skips tapping entirely and cuts its own thread in a pilot hole, which suits aluminum plates, cast parts and repair work where pre-tapping is the bottleneck. If the insert itself must never rotate under torque or vibration, neither is the specialist — the key-locking insert is.
When are key-locking inserts worth the extra installation effort?
When rotation is the failure mode. The locking keys are driven into the parent material specifically to stop the insert turning under repeated tightening, loosening or vibration — machine bases, fixture plates and high-load fastening points are the collected sources' examples. The cost is hole preparation: accurate dimensions followed by key setting per the manufacturer specification, more careful than a simple self-tapping installation. Where the risk is pull-out rather than rotation, the self-tapping branch is the lighter installation.
Can I use the same hole-preparation logic for heat-set inserts as for metal inserts?
No — the physics is different. A heat-set insert does not cut or tap anything: heat softens the surrounding thermoplastic, the plastic flows around the insert's external features, and the bond forms on cooling. So the plastic-side parameters govern — hole size, boss diameter, wall thickness and installation temperature — and overheating is a listed common mistake that deforms the component. Quote the parent plastic and process (3D print or injection moulding) on the RFQ so the insert geometry and insertion method are matched.
Individual insert specification pages
Each type has its own page — installation tables, material guidance and RFQ details.
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support