Difference Between Self-Tap & Sheet-Metal Screws

Application of Sheet Metal Screws

• The first and perhaps most important difference between a self-tapping screw and a sheet metal screw is that they are often used for very different purposes. A sheet metal screw can be used to keep more than one piece of metal together. However, it can also be employed when combining a piece of metal to a piece of wood. While it can also theoretically be used to hold two pieces of wood together -- thus metal is absent -- the reverse is not possible with a wood screw; the latter cannot be used to fasten pices of metal.

Use of Self-tapping Screws

• Self-tapping screws can be used for a wide variety of projects. Most often, they are used when you need a strong bond and the materials involved in the bond are dissimilar. For example, you might use a self-tapping screw to fix some broken furniture or to mount a piece of art to the wall. Dentists even use them in their work. Finally, self-tapping screws can prove particularly useful when connecting different pieces of plastics.

Form of the Sheet Metal Screw

• In some ways, the character of the sheet metal screw appears similar to the self-tapping. It is spiralled with threads. Usually these threads can be observed to run the whole length of the screw right down to its tip. At the opposite end of the screw is the head. This is frequently designed so the user can either remove it or screw it in with the aid of either a conventional wrench or screwdriver.

Self-tapping Design

• There are two essential designs for the self-tapping screw: thread-cutting and thread-forming. If you put a thread-forming screw into a material, it remolds that material to form paths for its threads as it advances. Alternatively, a thread-cutting screw actually takes away the material that lies in the way of its threads and removes it from the tapped space. In this sense, the thread-cutter operates very much like a machine tap. In either case, the point of the self-tapping screw is very sharp.