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Helical Inserts: How to Choose the Right One?

  • Writer: 翰君 陳
    翰君 陳
  • Nov 11
  • 4 min read

In metal, plastic, or aluminum parts, threaded holes can wear out and strip over time. That’s when a helical insert becomes the hero. A helical insert is a thread-reinforcement liner used to repair stripped threads or strengthen threads in softer base materials.


Put simply, it’s like cutting a fresh, durable thread inside the hole, so screws hold tighter and last longer.


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1) Functions & Benefits of Helical Inserts


In assembly and maintenance, a stripped thread is one of the most frustrating failures. Helical inserts solve this by restoring or upgrading the thread so the joint tightens securely and can be disassembled when needed.


Key benefits

  • Repair stripped holes: Rebuild a new internal thread when the original is damaged.

  • Prevent re-stripping: Let soft bases (aluminum, brass, plastics) withstand repeated fastening.

  • Increase thread strength: Stainless inserts handle higher torque—ideal for structural joints.

  • Wear & corrosion resistance: Suitable for high-temperature and high-vibration environments, extending service life.


So, it’s not only a repair piece—it’s a performance upgrade for the joint.

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2) Where Are Helical Inserts Used?


You’ve likely seen them without noticing. In aluminum housings, plastic shells, or zinc die-cast parts, threaded holes can loosen after repeated use. Adding a helical insert restores clamping force, often stronger than the original.


Common applications

  • Aluminum & zinc die-cast parts: Reinforce internal threads; avoid re-stripping.

  • Automotive & motorcycle engines/frames: Withstand vibration & heat; stay tight over time.

  • 3D-printed parts & plastic housings: Strengthen fastening points for repeated assembly.

  • Electronics & mold structures: Improve durability and serviceability.

  • High-temp / high-vibration settings: Machinery, compressors, heavy equipment.


In short: wherever screws tend to loosen over time, helical inserts can reinforce and extend life.


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3) Common Systems, Standards & Materials


Most metric helical inserts follow DIN 8140, but globally you’ll see metric, unified (UNC/UNF), and British (BSW/BSF) systems. They look similar but differ in pitch, flank angle, units, and use cases—they are not interchangeable.


Thread systems

System

Unit

Common Standards

Example

Features / Use

Metric

mm

ISO / DIN / JIS

M6 × 1.0

Mainstream in Taiwan, Japan, Germany; common for precision & general machinery.

Unified (UNC/UNF)

inch

ANSI / ASME

1/4-20 UNC / 1/4-28 UNF

Widely used in US, aerospace, automotive; 60° flank angle; modern, broad availability.

British (BSW/BSF)

inch

BS

1/4 BSW

Traditional UK machinery & service; 55° flank angle; gradually being phased out.


Key reminders

  • Metric ≠ BSW/BSF ≠ UNC/UNF — do not mix.

  • Repairing imported US/EU equipment? Confirm thread form (UNC/UNF, etc.).

  • Sheng Fong Precision supplies metric / unified / British series, in both coarse & fine pitch.


Insert materials

Material

Properties

Typical Use

SUS304

General corrosion resistance

Industrial use, mold repair

SUS316

Better acid/alkali & corrosion resistance

Semiconductor, chemical environments

Brass

Good conductivity, easy machining

Electronics, non-ferrous assemblies


Takeaway: Match standard + pitch + material to the application.

  • Outdoor or wet environments → SUS316

  • Electronics / plastic bosses → Brass

  • US-made equipment → verify UNC/UNF


Only when tolerance, pitch, and material are correctly matched will the insert deliver its full benefit.

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4) Coarse vs. Fine Threads



Helical Insert
Helical Insert



A frequent question: “What’s the difference between coarse and fine?”









Type

Characteristics

Best For

Coarse

Larger pitch; faster installation; more forgiving

General structures; aluminum & plastics (soft substrates)

Fine

Smaller pitch; more engaged threads; tighter lock

High vibration; precision joints; aerospace/mechanisms


Quick guide:

  • Coarse = speed & ease

  • Fine = tighter lock & vibration resistance


For high-load, high-vibration structures, fine is often preferred.For general maintenance & service work, coarse usually suffices.

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5) Extended Tips & FAQs


(1) Pairing recommendations

  • Fine insert + stainless screw: maximum clamping; great for high vibration / precision assemblies.

  • Coarse insert + aluminum base: higher tolerance to variation; fast field repair.


Rule of thumb: Fine favors stability; coarse favors efficiency. Tell us your base material and environment; we’ll recommend the pitch.


(2) Service cost differences


Fine threads tighten better but require higher machining precision and longer cycle time, so repair/replace costs tend to be higher. Coarse threads are faster with easier part sourcing.


Summary:

  • Precision / long-term fixed joints → Fine

  • Frequent service / temporary assemblies → Coarse


(3) Regional tendencies


Region

Typical Standards

Usage Trend

Taiwan / Japan / Germany

Metric (DIN 8140)

Precision machining & general machinery

USA / Canada

UNC (coarse), UNF (fine)

Aerospace, automotive, industrial

UK / some SE Asia (legacy)

BSW / BSF

Traditional machinery maintenance


Practical tip: On imported equipment, verify the thread form first (metric, UNC, UNF) before choosing an insert to avoid “goes in but doesn’t hold.”


(4) FAQ


  • Q1. Can I install helical inserts myself?

    Yes. Use the proper tools (tap, installation tool / tang driver) and keep the hole clean.


  • Q2. Can fine threads be used in aluminum or plastic?

    Not recommended. Fine pitch in soft substrates may not grip well—coarse is safer.


  • Q3. Can metric inserts work with unified screws?

    No. Different pitch/angle—this causes poor engagement or stripping.


  • Q4. My screw won’t go in—wrong pitch or stripped?

    New hole but screw won’t start = wrong thread form.Used hole gets looser over time = stripped → use a helical insert.


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6) Why Choose Sheng Fong Precision



Range: Helical inserts from M2 to M16, covering Metric (coarse/fine), Unified (UNC/UNF), and British (BSW/BSF).

Why us

  • Complete selection: Extensive inventory for immediate needs.

  • Consistent quality: Every lot inspected for pitch and dimensional accuracy.

  • Technical support: We help you identify thread form & choose the right spec.

  • Fast lead time: Small urgent orders and maintenance demands supported.


📩 LINE ID: @s9000 — We’ll help you select the optimal insert solution.


🛒 Full spec sheet: https://lihi3.me/9jPjQ




 
 
 

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