Thread-Forming Screws

Thread-forming screws create mating threads by displacing material rather than cutting it, producing no chips and a tight, vibration-resistant fit. The cold-formed threads work-harden the surrounding material, increasing strip-out resistance and making them ideal for plastics, die castings, and sheet metal where clean, repeatable threads matter. We stock thread-forming screws for both plastic and metal applications.

How Thread Forming Works

As the screw is driven, its specially profiled thread plastically displaces material to form a continuous, chip-free internal thread. Because no material is removed, the joint is stronger and more resistant to loosening than a cut thread, and the absence of chips makes these screws preferred in clean-assembly and electronics environments.

Types for Plastic

Screws designed for plastic use a wider thread angle and generous spacing to reduce hoop stress and prevent boss cracking. These high-low and 30-degree thread profiles maximize pull-out strength in soft and reinforced plastics while allowing higher seating torque before strip-out. They are the standard for enclosures, housings, and molded assemblies.

Types for Metal

For sheet metal and die castings, Type 25 (thread-cutting) and trilobular thread-forming designs displace metal to form strong, locking threads. The trilobular cross-section reduces driving torque and radial pressure, lowering the risk of cracking in castings while resisting back-out under vibration.

Materials and Finishes

Case-hardened steel with zinc plating: the standard, providing a hard forming surface and tough core. Stainless options are available where corrosion resistance is required, though hardened carbon steel forms threads more reliably in tougher materials.

Selecting the Right Thread-Forming Screw

Choose a plastic-specific thread form for molded bosses and a metal trilobular form for sheet and castings. Size the pilot hole precisely—thread-forming screws are sensitive to hole diameter, and the correct boss or hole size is critical to avoid strip-out or cracking. Verify the material is suitable for forming (ductile enough to displace) and select length for full thread engagement without bottoming out.

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