The ability of a screw to advance when turned while creating its own thread, versus, say, machine screws which require a pre-threaded nut or other female insert. Self-Tapping screws can cut their own threads as the screw is driven in to the material. Self-Tapping screws function by having a cutting edge which drills away the material, making a tiny hole for the screw to go into. This has nothing to do with the point of the screw but has everything to do with the threads which are designed to cut through the material.
There are two types of self-tapping screws: thread-cutting and thread-forming. A thread-cutting screw cuts material in its path as it is driven inward. These fasteners are normally made from stainless steel or carbon steel, and they see frequent use in wood and metal. Sometimes these screws can strip during disassembly because of the threads, so it is essential to repair this issue by using a slightly larger screw when you reassemble the project.
While thread-cutting screws remove some of the material as a user drives them, thread-forming screws deform the material as they are driven inward. Thread-forming screws are typically used in plastic. These screws cling tightly to the surrounding material, so ensure you tighten the screw the correct amount for a strong hold and intact material.
So how would you use self-tapping screws in metal, wood or plastic? Fortunately, these units function just like any other screw, meaning you drive them in with a screwdriver or a drill. If you drill a pilot hole for your self-tapping screw, you want to make sure that it is slightly smaller than the screw itself — if the hole is too big, the threads will not catch. You also want to ensure that the screw is positioned straight so that it aligns properly as you drive it in.
It is important to mention that the material you’re drilling should always be softer than the screw so that you don’t blunt the tip. The safest, and most common, type of self-tapping screw to use is stainless steel. This screw can penetrate many materials. Stainless steel screws have a strength ranging from 100,000 all the way to 150,000 tensile pounds per square inch (PSI).
These screws can typically hold around 80 to 100 pounds of weight, but the holding power depends on the length of the screw and the insertion angle. Self-tapping metal screws can become stronger with certain alloy compositions, depending on the amount of chromium or nickel.
Self-tapping screws are helpful in a variety of industries, with a few examples including:
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