What Is a Screw Thread Insert?
A screw thread insert is a component designed to create strong, durable threads in materials where direct threading is difficult or impractical. These inserts provide a way to strengthen or repair female threads in base materials that are too weak to support a tapped thread or where the existing thread has been damaged. Functioning much like a nut, they offer a threaded interior that mates with a corresponding male thread.
Thread inserts can also act as bushings to fill the gap between a bolt and the base material. Various types are available, often referred to by brand names such as E-sert, Helicoil, and Ensert, with specific types designed for use in metal or plastic substrates.
The drive for lighter components has led to the increased use of thread inserts, enabling the fastening of lightweight materials without sacrificing thread strength or integrity.
Applications of Screw Thread Inserts
Thread inserts are particularly useful in materials with low strength, like plastics, where creating durable internal threads for screw fastening is challenging. While self-tapping screws can be used after drilling a pilot hole, they may not support repeated disassembly and reassembly, making thread inserts a preferred solution for maintaining thread integrity.
In metal parts, thread inserts are beneficial for small-diameter threads (e.g., M3) or where minimal thread engagement is available, as they help prevent damage from over-tightening. They are also an effective solution for repairing stripped or damaged threads, allowing for the restoration of the original thread size and strength.
Principle of Screw Thread Inserts
Screw thread inserts, such as coiled E-serts and Enserts for metal, are installed into a pre-tapped hole using a special tool or directly screwed into a drilled hole, respectively. This process creates a durable female thread in the base material. E-serts, for example, may require careful handling to prevent dislodgement through repeated use, whereas Enserts offer stronger threads and are commonly used for repairs.
Types of Screw Thread Inserts
1. Coil Type
The coil type is a popular choice, made from coiled wire that easily accommodates pitch variations, providing flexibility in application.
2. Self-Tap Type
Self-tap inserts eliminate the need for pre-tapped holes, allowing direct insertion into a prepared hole, and simplifying installation.
3. Press-Fit Type
Press-fit inserts do not require screwing but are instead secured through press-fitting into the base material, offering a permanent solution.
Using Screw Thread Inserts
How to Install Screw Thread Inserts
Installation typically involves four steps, though specific procedures can vary by insert type. First, drill a hole of the correct diameter for the insert. Next, tap a thread into the hole if necessary. Then, verify the threading with a gauge to ensure compatibility. Finally, insert the thread, completing the process with any necessary finishing touches, such as removing installation tabs.