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Self-Tapping vs Self-Drilling Screws: The Unknown Differences

The Eternal Question...  
For such commonly-used fasteners, the confusion in features and application of both self-tapping and self-drilling screws is equally common. And between the two screws, the vernacular is often confused, with the name for one being used for the other.  

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So, let’s set the record straight. Here are the differences between both fasteners. To summarise:

Self-Tapping – a screw for securing thinner sheet metals and other substrates that cuts its own thread, but usually requires a predrilled or pre-punched hole.

Self-Drilling – a screw that can, well, self-drill through various gauges of metal materials without predrilling.

Both – perfect for securing two materials—steel to steel or steel to timber—for when a better hold compared, to nuts and bolts, is required.

To elaborate, here are the finer facts:

Self-Tapping

  • Creates its own thread while turning, therefore it does not need matching female threads, like those in a nut from a nut/bolt set or machine screws.
  • Can also be used in wood and softer substrates like some plastics.
  • This screw features a Type AB point.
  • To remember it when you see it, this screw has a point “like a pencil”.
  • Most common uses –

-       1 and 2-layer thin gauge sheet metal securing

-       Fastening of aluminium sections to each other and into screw flutes.

-       Screwing into plastic housings.

-       Fixing metal brackets into ply and timber.

Self-Drilling

  • With a point “like a drill bit”, these screws create their own hole, and their own thread in one action. This is probably where the confusion with self-tappers comes in – both kinds of screws are technically self-tapping as far as the function of their threads are concerned, but the massive difference is in the function of their points.
  • Self-drillers can be characterised as a fine thread or a coarse thread, self-tappers can’t.
  • In short, self-tappers can’t drill, self-drillers can as well as tap a thread.
  • Self-drillers are also commonly called ‘Tek’ screws, a proprietary brand name associated with their unique shape and function.
  • Drill point sizes dictate drilling capacity. Common Tek point sizes are #2, #3, #4 and #5 (Series 500) – 2 and 3 most common, 4 and 5 for going through thicker metal.
  • Most common uses –

-       Cladding and metal roofing

-       HVAC – duct, clips and brackets

-       Carports/sheds/garages

-       General construction

-       Steel framing

 

Do you have any questions about the application of these screws for what your are doing? Get in touch with the leaders in All Things Fixings now.