Self Drilling or Self Tapping Screws?

There can be a bit of confusion when ordering screws for your project. Most of the time this is due to the terminology or nomenclature being misunderstood. We would like to help you understand some of the differences associated with various types of screws.

Self Tapping Screws
Many times a customer will ask us for a “Self Tapping Sheet Metal Screw” but what they really want is a “Self Drilling Sheet Metal Screw” The difference is that a Self Driller will cut a properly sized hole in the metal and then tap the metal by forcing its own threads through the metal.  In reality a Self Drilling Screw is also A Self Tapping Screw as it performs both functions. A Self Tapping Screw on the other hand, will tap its own threads through the sheet metal but a hole must be already present.

As with anything there are some variations or exceptions to the rule. A sheet metal screw may also be designated as “Self Piercing”. In this case the screw has a significantly sharper point and hardness. It is capable of piercing its own hole in thin metal so that its threads may start into the opening and enlarge and tap the hole as well.

These are the general guidelines that apply to sheet metal, which is different than metal which is thicker. Often, sheet metal is about the same hardness as a sheet metal screw, so the screw is not actually “cutting“ its own threads but rather it is simply forcing itself through the metal by the force of the threads pulling it through a small hole about the size of the root diameter of the screw. Because the metal being “tapped “ is thin the threads are not actually “cutting “ the sheet metal, rather the sheet metal is riding between the threads of the screw and therefore the screw does not have to be much harder than the sheet metal itself.

Self Drilling Screws
All of this changes when the metal being “tapped” is thicker than sheet metal. In this case the screw must be significantly harder than the metal being tapped, and the thread design must be such that it can clear the hole of the material debris that is actually being cut by the threads The hole size is also critical for this type of self tapping operation. The most common type of screw is the Type F thread design.

Metal is not the only material that might be tapped by a screw. There are screws that tap concrete and plastic and wood just to name a few.

There are volumes of technical data written pertaining to the topic of drilling and tapping. Power Bolt and Tool is a company that is dedicated to helping you choose the Right Fastener for your project. We will help you get it to the Right Place at the Right Time. Call one of our experts today and let us help you get it done right.
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