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What is the Difference Between Self-Tapping Screws & Self-Drilling Screws?

Self Drilling and Self Tapping Fasteners in ApplicationWhen it comes to deciding the correct screw for the job, it is important to make sure you are using the correct terminology. Many end users tend to confuse the descriptive phrase self-tapping and self-drilling. This can lead to the purchase of the incorrect fastener for the job.  Below is a guide describing what makes self-drilling and self-tapping screws different and what they are used for respectfully. This blog aims to assist our end users in finding the correct fastener they are looking for and ensure a more accurate selection and purchase the first time. Saving both time and money! The confusion often stems from the fact that self-drilling screws are often also self-tapping in that a self-drilling screw "taps" it's hole once drilled, while self-tapping screws require a predrilled hole. What else makes these two commonly used fasteners unique?


Self Tapping Screw Point in Application and Installation

Self-Tapping Screws

  • Requires a pre-drilled hole.
  • Self Tapping Screw Point with Wings FastenerCreates / "Taps" threads in pre-drilled hole during installation (As shown in Figure 1)
  • Comes in 3 “Types”:
  • Type A – Coarse Thread, Gimlet point
  • Type AB – Fine Thread, Gimlet point
  • Type B – Fine Thread, Blunt point (also available in high-low thread)
  • Utilizes a spaced thread design
  • Commonly used in a variety of soft or thin material:
  • Sheet metal, Wood, and plastic – HVAC, wood working, furniture assembly
  • Abbreviated as STS (Self Tapping Screw) and SMS (Sheet Metal Screw)
  • Available in a variety of Drives, Head Styles, Materials and Finishes


Self Drilling Screw Point Fastener in Application and Installation

Self-Drilling Screws

  • No pre-drilled hole required – fastener uses its drill point to remove material.
  • Self Drilling Screw Point FastenerCreates / "Taps" threads after drilling hole, during installation
  • Threads cannot be formed until the hole has been completely drilled through entire material: (As shown in Figure 2)
  • Speed is needed in order for a hole to be drilled and drilling needs to be completed before tapping otherwise threads will become damaged or "stripped"
  • Figure 2: Shows that L1 > L2 AKA Drill point > Material Thickness 
  • Comes in 2 “Types”:
  • Spaced Thread - Referred to as "BSD" - (similar to Type A threads of a self-tapping screws).
    • Should be treated as a sheet metal screw with a drill point and are used to drill through thin metals.
    • Most common self-drilling screw is a Hex Washer Head BSD style screw.
    • (Recommended Thicknesses For "BSD" Self-Drilling Screws Shown in Figure 4)
  • Machine Screw Thread - Referred to as "CSD"
    • Have a longer drill point with a machine screw cutter and machine screw threads. 
    • Can be used to drill into thicker materials due to machine screw thread being able to withstand a higher pull out force.
    • (Recommended Thicknesses For "CSD" Self-Drilling Screws Shown in Figure 5)
  • Advantage of efficiency - Self-drilling screws can create their own pilot holes, they can save you time and effort compared to self-tapping screws that require pre-drilling
  • Drill point sizes range from #1 - #5 - a higher number denotes a higher thickness capability.
  • Commonly used in metal roofing, construction, and other heavy-duty applications.
  • Available with sealing washers (bonded NEO washers and bonded rubber sealing washers)
  • Chips or shavings are always created by self-drilling screws:
  • Should not be used when close to electronics - can cause a short or damage electronics.
  • It is not recommended to use a magnetic bit or socket during installation.
    • A magnet will attract debris to the head of a fastener; preventing the head of the fastener from being flush in final position
  • Abbreviated SDS (Self Drilling Screws) or referred to as “Self-Drillers” “Drill Screws” or by the brand name “Teks® Screws”


Self Drilling Screw Point with Wings Fastener in Application and Installation

Self-Drilling Screws with Wings

  • A self-drilling screws with an additional feature knows as "wings“  or "reamers".Self Drilling Screw Point with Wings Fastener
  • Used almost exclusively when attaching wood to metal
  • Wings – Bore out a larger diameter, clearing out additional material, preventing the fastener from threading before drilling is completed. (As shown in Figure 3)
    • ​This allows for ignoring the material that is bored out during instillation, decreasing the total material thickness.
  • Designed to break off when contacting secondary material in application. (Ex. Bores through wood, breaks off on metal, taps threads in metal)


Recommended Min-Max Material Thicknesses For Self-Drilling Screws

Spaced Screw Thread Chart


Machined Screw Thread Chart


Drill Tek Point Material Thickness


The most important thing to remember when deciding if you need a self-drilling vs. a self-tapping screw is whether you are using a pre-drilled hole or require the fastener to do the drilling in your application. It is essential to understand the difference between self-drilling and self-tapping fasteners to ensure you are using the right type of screw for your specific job. Self-drilling fasteners are designed to drill their own pilot holes, while also tapping threads. Self-tapping fasteners require a pre-drilled hole prior to the fastener being driven into a work piece and "tapping" its threads. Next time you're in need of fasteners, make sure to use the correct terminology and choose the right type of screw for your specific application. With the right knowledge, you can confidently select the appropriate fasteners, saving time and effort.


Key Take-aways for Self-Drilling and Self-Tapping Fasteners

Self-Tapping Screws
  • Require a pre-drilled hole
  • Creates threads (taps threads) in pre-drilled hole during installation
  • Utilizes a spaced thread design
  • Comes in 3 “Types”
    • Type A - Coarse Thread, Gimlet point
    • Type AB - Fine Thread, Gimlet point
    • Tpe B - Fine Thread, Blunt point
  • Commonly used in soft or thin material
  • Sheet metal, wood, and plastic
  • Abbreviated as STS or SMS
Self-Drilling Screws
  • No pre-drilled hole required
  • Drills its own hole prior to tapping threads
  • Comes in 2 “Types”
    • BSD - Spaced Thread
    • CSD - Machine Screw Thread
  • Drilling point (#1-#5)
  • Used in metal roofing, construction, and other heavy-duty applications
  • Abbreviated SDS or called brand name TEK ®
  • Available with Wings for wood to metal applications


Self-Tapping Self Drilling and Self-Drilling Screws with wings Overview

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Wednesday, January 31, 2024