GB/T24425.1 Thread inserts, wire thread inserts

What are Wire Thread Inserts?

In the precision-driven world of modern manufacturing, Wire Thread Inserts (commonly known as Helicoils or Screw Thread Inserts) are vital components used to create high-strength internal threads in materials with low shear strength. At Ever Power, we provide inserts compliant with the GB/T 24425.1-2009 standard, designed to repair damaged threads or reinforce new ones in aluminum, magnesium, copper alloys, and engineering plastics.

By effectively distributing stress over a larger area of the parent material, these inserts provide a wear-resistant, high-temperature, and corrosion-resistant thread that significantly extends the service life of expensive mechanical components.

Technical Breakdown: GB/T 24425.1 Dimensional Standards

Understanding the geometry of a wire thread insert is critical for proper installation. Unlike standard nuts, these inserts have a “free state” diameter ($D_z$) larger than the hole they inhabit, allowing them to exert outward spring pressure that locks them securely in place.

1. Precision Miniature Range (M2 to M5)

For delicate electronics and precision instruments, small-diameter inserts must adhere to strict pitch and diameter limits:

• M2: Features a standard coarse pitch of 0.4mm. In its free state, the diameter ($D_z$) ranges from a minimum of 2.53mm to 2.85mm.
• M3: Utilizes a 0.5mm pitch. The free state diameter ($D_z$) expands to between 3.8mm and 4.2mm.
• M5: A common industrial size with a 0.8mm pitch. The free state diameter is significantly larger, ranging from 6.25mm to 6.85mm to ensure a robust grip after compression.

2. Standard Industrial Range (M6 to M12)

This range represents the “workhorse” of automotive and aerospace assembly. Key parameters include the Guide Ring Diameter ($F$), which ensures the insert enters the tapped hole squarely.

• M6: 1.0mm pitch. The guide ring diameter ($F$) is held between 7.28mm and 7.58mm, with a free state diameter reaching up to 8.0mm.
• M10: 1.5mm pitch. The guide ring diameter ($F$) is 11.82mm to 12.1mm. The free state diameter expansion reaches a maximum of 13.0mm.
• M12: 1.75mm pitch. $F$ values range from 14.2mm to 14.5mm. These are critical for structural engine mounts and heavy machinery housings.

3. Heavy-Duty Structural Range (M14 to M39)

For large-scale infrastructure and heavy equipment, these inserts handle massive torque loads:

• M16 to M22: Standardization usually follows a 2.0mm to 2.5mm pitch. For instance, an M20 insert features a guide ring ($F$) between 23.01mm and 23.46mm.
• M30 to M39: High-torque applications. An M30 uses a 3.5mm pitch with a guide ring ($F$) of 34.1mm to 34.7mm. The largest standard size, M39, features a 4.0mm pitch and a guide ring ($F$) reaching up to 44.33mm.

Material Science: The 304 Stainless Steel Advantage

At Ever Power, our standard wire inserts are manufactured from high-quality 304 Stainless Steel (Cr-Ni steel). This material choice is not arbitrary; it offers a specific set of mechanical benefits:

• Work Hardening: The cold-rolling process used to shape the wire increases the tensile strength of the stainless steel, making the resulting thread much harder than standard machine-cut threads.
• Corrosion Resistance: Ideal for marine, chemical, and outdoor environments where moisture would otherwise lead to “thread welding” or rusting in carbon steel assemblies.
• Thermal Stability: 304 stainless steel retains its structural integrity at elevated temperatures, preventing the “creeping” of threads in hot machinery.

Installation Excellence: The Step-by-Step Process

Correct installation is the difference between a permanent fix and a failed assembly. Ever Power recommends the following workflow:

Step 1: Precision Drilling

Use the specific drill bit size designated for the insert (e.g., for M6, the drill size is slightly larger than 6mm to accommodate the wire thickness).

Step 2: Specialized Tapping (STI Tap)

Standard taps will not work. You must use an STI (Screw Thread Insert) Tap, which cuts a thread larger than the nominal size but with the same pitch.

Step 3: Winding and Tang Removal

The insert is wound into the hole using an installation tool. Once seated, the “Tang” (the driving crossbar at the bottom) is snapped off at the pre-cut break-off notch (identified as parameter $a$ in GB standards) using a punch tool. This ensures the screw can pass through the entire length of the insert.