Slotted Thread Insert (Threaded Insert) – Product Introduction

The slotted thread insert is a self-tapping threaded bushing defined as a “threaded plug” in the German standard DIN 7965. It is a hollow cylindrical body with internal and external threads, featuring a straight slot cut into the top end. During installation, the slotted head is driven into a pre-drilled hole using a dedicated tool or screwdriver; the external threads self-tap and cut into the parent material, forming a strong mechanical interlock. Standard bolts, spark plugs, or other fasteners can then be threaded into the insert. It can restore damaged internal threads or significantly enhance the strength and wear resistance of threaded holes in low-strength materials such as aluminum alloys and cast iron.

I. Product Features

Self-tapping external threads: No pre-tapping required — simply screw into a pre-drilled hole to cut matching threads in one step.

Straight slot at the head: Works with dedicated installation tools or screwdrivers; installation can be performed manually or pneumatically with ease.

Integrated internal and external threads: The external threads lock into the parent material while the internal threads accept bolts, providing a high-strength standard internal thread interface.

Available in carbon steel and stainless steel: Standard material is high-strength free-cutting carbon steel (blackened or zinc-plated); 304/A2 and 316/A4 stainless steel variants are also available for corrosion resistance.

Standard thread specifications: Internal threads are standard metric coarse pitch (M); external threads are oversized-pitch threads specifically designed for self-tapping applications.

II. Product Advantages

Strong repair capability: Stripped or damaged threaded holes can be restored to their original standard thread size by reaming and inserting the thread insert, allowing continued use of the original fasteners.

Enhanced performance in low-strength materials: Installing a steel thread insert into soft substrates such as aluminum, zinc alloy, or plastic dramatically increases thread connection strength and wear life, and withstands repeated assembly and disassembly.

Fast and cost-effective installation: After drilling the pilot hole, simply screw the insert in — eliminating the complex tooling required by traditional bushings; each insert installs in seconds.

No expansion stress: Unlike some expansion-type inserts, self-tapping inserts lock through thread engagement and do not exert outward expansion pressure on the parent material, making them safer for thin-walled or sensitive components.

High-temperature resistance and anti-seizure performance: Steel thread inserts are particularly suited for high-temperature locations such as spark plug holes, effectively preventing seizure between bolts and aluminum alloy cylinder heads.

III. Application Areas

Automotive repair and modification: Restoring spark plug thread holes in aluminum cylinder heads, valve stem threads, and drain plug holes in oil pans.

General machinery and engines: Pre-installing inserts in aluminum alloy or cast iron housings to enhance the durability of critical threaded holes, such as in transmission cases and engine accessory bracket connections.

Molds, tooling, and fixtures: Creating high-strength, frequently disassembled threaded points in aluminum molds, nylon, or aluminum alloy fixtures.

Electronics and precision instruments: Inserting into plastic or light-alloy enclosures to provide reliable metal threads for cover plates and connector attachments.

Industrial equipment maintenance: Restoring worn threads in water pumps, air conditioning compressors, and pump/valve housings caused by repeated assembly and disassembly.