--- title: "What Are Helical Thread Inserts Used For?" description: "Helical Thread Inserts (DIN 8140) are used for reinforcing or repairing threads in aluminum, magnesium and plastics. Catalogued M3 to M20." url: https://engineeringhardware.com/applications/helical-thread-inserts/ source: Engineering Hardware & Fasteners --- # What Are Helical Thread Inserts Used For? Threaded Inserts · DIN 8140 · Application guide Typical applications, the industries that specify helical thread inserts, and how to choose the right size, material and finish for the joint. Helical Thread Inserts are used for reinforcing or repairing threads in aluminum, magnesium and plastics. They are manufactured to DIN 8140, and selection is driven by the thread size, the fit and tolerance the assembly requires, and the service environment. - **Primary duty:** Reinforcing or repairing threads in aluminum, magnesium and plastics - **Governing standard:** DIN 8140 - **Thread size range:** M3 to M20 - **Category:** Threaded Inserts Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation. ![What Are Helical Thread Inserts Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/06/Helical-Thread-Inserts-—-DIN-8140.webp) Helical Thread Inserts (DIN 8140) are specified where the joint requires reinforcing or repairing threads in aluminum, magnesium and plastics. The sections below cover the typical end-uses by industry, the size and material decisions for each, assembly practice, and the applications this fastener type is not suited to. Stocked across roughly M3 to M20, they cover general to heavy-duty work. ## Typical Applications for Helical Thread Inserts The most common settings where these are specified: - **Aerospace & motorsport:** lightweight alloy parts needing full-strength steel threads. - **Field repair:** recovering a stripped thread without scrapping the part. - **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment. - **Maintenance & repair (MRO):** a stocked size for servicing existing plant where the original fastener spec must be matched. - **Fabrication & metalwork:** bench and on-site assembly of steel frames, enclosures and weldments. ## How to Specify Helical Thread Inserts for Your Application - **Size:** Match the nominal size to the mating thread or hole. This product spans M3–M20; check the full table below for the exact dimensions of each size. - **Tap & length:** Drill and tap to the specified STI size, and pick insert length (commonly 1.5×D or 2×D) for the load and parent material strength. - **Environment:** For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient. - **Standard:** This product is supplied to DIN 8140. Quoting the standard on your order guarantees interchangeable dimensions between suppliers. ## Installation & Assembly Practice - Drill and tap with the specified STI tap — a standard tap will not produce the correct thread for the insert. - Install to the specified depth (typically 0.25–0.5 mm below the surface) and remove the tang where the design requires it. ## Common Selection Mistakes with Helical Thread Inserts - Fitting an insert into strong steel that already holds a thread — added cost for no gain. - Skipping the tang removal, which then blocks the mating screw. ## Where Helical Thread Inserts Are Not the Right Choice Not a fix for a hole that is already oversized beyond the STI tap range, and not needed in steel that already holds a thread well. Custom manufacturing · Made to drawing ## Need a helical thread inserts outside the standard range? Thread size, body length, knurl or key form and installation method are all variable against the parent material. Made by tapping or knurling. Minimum order from 2,000 pieces; samples within 7 days of drawing approval. [Custom threaded insert manufacturing](https://engineeringhardware.com/custom/inserts/)[Send a drawing](https://engineeringhardware.com/custom/inserts/#rfq) ## Technical Drawing Dimensioned line drawing of M3 Helical Thread Inserts to DIN 8140. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected. - **Pitch (mm):** 0.5 - **Length (mm):** 4.5 - **Drill / tap size (mm):** 3.1 (STI tap) - **Free coil diameter (mm):** 3.45 - **Notes:** Wire thread insert, 1.5xD length; tang break-off ## Dimensions & Specifications (DIN 8140) | Thread size | Pitch (mm) | Length (mm) | Drill / tap size (mm) | Free coil diameter (mm) | Reference standard | Notes | | --- | --- | --- | --- | --- | --- | --- | | M3 | 0.5 | 4.5 | 3.1 (STI tap) | 3.45 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M3 | 0.5 | 6.0 | 3.1 (STI tap) | 3.45 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M4 | 0.7 | 6.0 | 4.2 (STI tap) | 4.57 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M4 | 0.7 | 8.0 | 4.2 (STI tap) | 4.57 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M5 | 0.8 | 7.5 | 5.3 (STI tap) | 5.67 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M5 | 0.8 | 10.0 | 5.3 (STI tap) | 5.67 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M6 | 1.0 | 9.0 | 6.3 (STI tap) | 6.80 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M6 | 1.0 | 12.0 | 6.3 (STI tap) | 6.80 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M8 | 1.25 | 12.0 | 8.4 (STI tap) | 9.01 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M8 | 1.25 | 16.0 | 8.4 (STI tap) | 9.01 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M10 | 1.5 | 15.0 | 10.5 (STI tap) | 11.26 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M10 | 1.5 | 20.0 | 10.5 (STI tap) | 11.26 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M12 | 1.75 | 18.0 | 12.6 (STI tap) | 13.51 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M12 | 1.75 | 24.0 | 12.6 (STI tap) | 13.51 | DIN 8140 / ISO 10130 | Wire thread insert, 2xD length; tang break-off | | M16 | 2.0 | 24.0 | 16.5 (STI tap) | 17.71 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | | M20 | 2.5 | 30.0 | 20.5 (STI tap) | 22.07 | DIN 8140 / ISO 10130 | Wire thread insert, 1.5xD length; tang break-off | Inside the plant ## Manufactured in our own plant This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided. 1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift. 2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g. 3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1. 4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227. ## Frequently Asked Questions ### What are Helical Thread Inserts used for? Reinforcing or repairing threads in aluminum, magnesium and plastics. They are supplied to DIN 8140. ### Which industries use Helical Thread Inserts? They are commonly specified in general machine building, maintenance & repair (mro) and fabrication & metalwork, among other sectors. ### How do I choose the right size of Helical Thread Inserts? Match the nominal size to the mating thread or hole. This product is available from M3 to M20; the full dimension table on this page lists each size. ### When should I use Helical Thread Inserts instead of tapping directly? Use them in soft alloys, plastics or thin sections where a cut thread would strip, or to repair a stripped hole. In strong steel that already holds a thread well, they are usually unnecessary. ### Can I get a quote for Helical Thread Inserts in the size and material I need? Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time. ## Related Pages Product page: [Helical Thread Inserts — specifications & sizes](https://engineeringhardware.com/fastener/helical-thread-inserts/) ### Helical Thread Inserts Specification Guides ### Related Fastener Applications