Our threaded inserts and insert kits create strong, durable threads in soft or damaged material. Helical wire inserts reinforce and repair threads in metal, self-tapping inserts add metal threads to plastic and alloy, and press-fit inserts strengthen wood and composites. Complete kits include the insert, tap, and installation tool.

Threaded Inserts & Insert Kits - Metric Sizes

What Is a Threaded Insert?

A threaded insert is a component that provides a strong, wear-resistant internal thread inside a softer, weaker, or damaged host material. In soft metals such as aluminium, or in plastics and wood, a thread cut directly into the parent material can strip under load or after repeated assembly. An insert places a hardened steel or brass thread into the component, distributing load over a larger area and delivering a durable, reusable thread that far outlasts the base material.

At Metric Specialties we stock the main insert families. Helical wire inserts (often known by the trade name Helicoil) are coiled stainless wire that screws into a specially tapped hole, forming a resilient thread ideal for repairing stripped threads or reinforcing high-load holes in alloy. Self-tapping (solid) inserts cut their own thread as they are driven into plastic or soft metal, providing a robust metal thread. Press-fit, heat-set, and moulded-in inserts suit plastics and composites. Complete thread repair kits bundle the inserts with the correct tap and installation mandrel for a ready-to-use solution.

Key Features and Benefits

• Thread Repair: Helical inserts restore stripped or damaged threads to original strength without replacing the component.
• Reinforced Threads: Inserts distribute load over a larger area, creating durable threads in soft alloys and plastics.
• Reusable Assembly: Hardened insert threads withstand repeated assembly far better than threads cut in soft material.
• Material Versatility: Solutions for aluminium, plastic, wood, and composites across wire, self-tapping, and press-fit types.
• Complete Kits: Repair kits include insert, tap, and tool for a fast, self-contained installation.

Materials and Finishes

• Stainless Steel Wire Inserts: Corrosion-resistant helical inserts for thread repair and reinforcement.
• Steel Self-Tapping Inserts: Hardened solid inserts that cut their own thread in plastic and soft metal.
• Brass Inserts: Heat-set and press-fit inserts for plastics and electronics enclosures.

Standards Compliance

• DIN 8140 — Helical coil thread inserts.
• ISO 261 — ISO metric screw threads for inserting internal threads.

Common Applications and Industries

Threaded inserts are widely used in automotive, aerospace, and machinery repair to restore stripped threads in aluminium castings such as engine blocks, cylinder heads, and gearboxes, avoiding costly component replacement. In manufacturing, inserts reinforce high-load threaded holes in soft alloys, ensuring durable, reusable threads that survive repeated assembly.

The electronics and plastics industries rely on heat-set, press-fit, and self-tapping inserts to add strong metal threads to moulded enclosures, housings, and panels, where a thread cut directly into plastic would strip. Furniture, appliance, and consumer-product makers use inserts for knock-down fittings and durable fastening points in wood and composites, combining strength with easy assembly and disassembly.

How to Choose the Right Insert

Match the insert to the host material and task: helical wire inserts repair and reinforce threads in metal, self-tapping (solid) inserts add metal threads to plastic and soft metal without pre-tapping, and heat-set or press-fit inserts suit moulded plastics and composites. For thread repair, confirm the insert size matches the original fastener thread.

Consider whether you need a complete kit — our thread repair kits include the insert, the correct insert-specific tap, and the installation tool for a self-contained solution. Choose the material for the environment, favouring stainless helical inserts and brass inserts for corrosion resistance, and follow the correct drilling, tapping, and installation sequence for a reliable, full-strength thread.

Size Range and Availability

Available in M3 through M20 across helical wire, self-tapping, and press-fit inserts, individually or as complete thread repair kits with tap and tool.

Why Buy From Metric Specialties

As dedicated metric fastener specialists, we hold threaded inserts & insert kits in the sizes, grades, and finishes that engineers actually need, backed by clear DIN and ISO standard references so you can specify with confidence. Every item is sourced to recognised standards and quality-controlled, giving you consistent thread fit, strength, and corrosion performance across repeat orders.

Whether you need a single item for a repair or bulk quantities for production, our range, technical guidance, and fast dispatch help you find the exact fastener for the job. If you are unsure which size, grade, or finish suits your application, our team can help you match the right product to your load, environment, and standard, so your assemblies are reliable and built to last.

Frequently Asked Questions (FAQs)

1. What is a threaded insert used for?

A threaded insert provides a strong, durable internal thread in a soft, weak, or damaged material such as aluminium, plastic, or wood, and is widely used to repair stripped threads or reinforce high-load holes.

2. What is a helical wire insert (Helicoil)?

A helical wire insert is a coil of stainless wire that screws into a specially tapped hole to form a resilient internal thread. It repairs stripped threads and reinforces holes in soft alloys.

3. How do I repair a stripped thread with an insert?

Drill out the damaged thread, tap the hole with the insert-specific tap, then wind the helical insert in with the installation tool. The insert provides a fresh, full-strength thread in the original hole.

4. What is the difference between a wire insert and a self-tapping insert?

A wire insert is a coil fitted into a pre-tapped hole, while a self-tapping (solid) insert cuts its own external thread as it is driven in. Self-tapping inserts suit plastics and soft metals without pre-tapping.

5. What inserts are best for plastic?

Heat-set, press-fit, and self-tapping brass inserts are commonly used in plastics, providing a durable metal thread that resists stripping and pull-out in enclosures and moulded parts.

6. Do your insert kits include the tap and tool?

Yes. Our complete thread repair kits include the inserts, the correct insert-specific tap, and the installation mandrel or tool, so everything needed for the repair is in one package.

7. Are threaded inserts reusable?

The insert itself provides a durable thread that withstands many assembly cycles far better than a soft-material thread. The insert stays in place; the mating bolt is what is fitted and removed repeatedly.

8. Can inserts strengthen threads in aluminium?

Yes. Fitting a stainless helical or steel insert into an aluminium component distributes load over a larger area and provides a hardened thread that resists stripping under high torque or repeated use.

9. What size inserts do you stock?

We stock M3 through M20 across helical wire, self-tapping, and press-fit inserts, available individually and as complete thread repair kits.

10. How do I remove a helical wire insert?

A helical insert is removed with a dedicated extraction tool that grips the coil and winds it out. The hole can then be re-tapped and a new insert fitted if required.