Types of Self-Tapping Screws

Updated February 21, 2017

Self-tapping screws bore through and deform both plastic and metal materials. With the capability to cut material and create threads, self-tapping screws, also called "self-tappers," remove the steps of pre-drilling and tapping from many building and machining projects. With an understanding of the appearance and application of different types of self-tapping screws, the builder can choose the right one for each project.

Thread-Forming Screws

The thread-forming type of self-tapping screw creates threads by deforming a substrate, typically soft metal or plastic. From a distance, the thread-forming screw's shank appears similar to a machine screw's shank; perfectly cylindrical with closely grouped threads. However, upon closer inspection, the thread-forming screw's shank slightly tapers toward the end. Despite its taper, the thread-forming screw's tip does not form a sharp point. Many thread-forming screws have a wedge-shaped incision at their tip. The sharpened edges of the incision begin to embed the screw's threads into the substrate and begin the thread-forming process. Depending on the relative hardness of the substrate material, thread-forming screws might require pre-drilling.

Thread-Cutting Screws

The thread-cutting screw creates threads by cutting and removing the substrate material, usually soft metal or plastic. The thread-cutting screw appears similar to a wood screw; its shank typically tapers to a sharp point. The extra-sharp, angled threads surrounding the thread-cutting screw's shank cut into the substrate and push waste material from the hole. During the cutting process, the screw's sharp threads create a corresponding set of threads in the substrate material. Construction professionals often refer to thread-cutting screws as self-drilling screws.

Self-Tapping Screw Heads

Construction professionals and machinists frequently classify thread-cutting and thread-forming screws according to their head type. Self-tapping screw heads vary according to two general characteristics: shape and drive. Shape refers to both the form and size of a self-tapping screw. Hexagonal heads are called "hex head" screws, flat-topped, tapered heads are called "countersunk" heads and rounded heads are called "round" or "pan" heads. Drive refers to the type of screwdriver bit used to twist the screw. Self-tapping screws are available as Phillips drive, slotted driver, star, square and hex drive.

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About the Author

Based in Hawaii, Shane Grey began writing professionally in 2004. He draws on his construction experience to write instructional home and garden articles. In addition to freelance work, Grey has held a position as an in-house copywriter for an online retailer. He holds a Bachelor of Arts in theater arts from Humboldt State University.