Self-Drilling Screw Manufacturing Process
The term “TEK screw” originates from an original trademarked brand of self-drilling screws manufactured in Australia. Over time, similar to how the brand name Kleenex has been used informally as a genericized trademark for facial tissue, TEK screws became a well-known name for any screw with a self-drilling tip, especially within the building and construction industry.
TEK screws, or self-drilling screws, is a combination of 3 functions in-one – Drilling, Tapping (forming threads), and Fastening, which are performed simultaneously and in one single operation.
What distinguishes TEK screws from other fasteners is their built-in drill bit tip, which can range in size and length depending on the application. This seemingly small feature drastically affects how the screw performs, especially in different materials and thicknesses.
One of the primary reasons TEK screw size matters is structural integrity. A screw that is too short may not fully penetrate the base material, compromising the load-bearing capability of the joint. Conversely, a screw that is too long may punch through the other side or become loose over time due to inadequate thread engagement.
For instance, attaching a steel roofing sheet to a metal purlin requires a screw that can penetrate both the sheet and the purlin, while still allowing for several threads to grip the base material. If the screw is undersized in either length or diameter, it can result in:
On the other hand, if the screw is oversized in either length or diamter, it can result in:
In structural applications, these failures can be catastrophic.
In terms of size, the following components that would influence the size and in turn, the performance of the TEK screw are:
TEK screw sizes are typically identified by:
Gauge refers to the outer diameter of the screw shank (measured in inches). Common TEK screw gauges include:
The higher the number, the thicker the screw.
Screw length is measured from the tip of the drill point to the bottom of the head on Hex headed screws, and to the top of the head for flat headed screws such as Truss head screws or CounterSunK (CSK) screws. Typical TEK screw lengths range from:
According to Australian AS3566.1 standards, self-drilling screws intended for drilling and tapping into layered or unlayered steel with a minimum total thickness of 0.9 mm are classified into three types: ASD, BSD, and CSD.
ASD and BSD screws feature spaced threads, while CSD screws use UNC machine screw thread profiles with a 60-degree standard thread form.
The drill points are designated as No. 2, No. 3, and No. 4 for ASD, BSD, and CSD screws respectively, each suited for different panel thicknesses.
TEK screws are rated from No. 1 (TEK 1) to No. 5 (TEK 5), with the number indicating the drill capacity—the maximum thickness of steel the screw can penetrate without pre-drilling.
The following table lists the maximum material thickness each size designation is capable of drilling through prior to thread pick-up. The material thickness includes single, double and spaced material layers.
| Size designation | Type ASD (Point No. 2) | Type BSD – Point No. 2 | Type BSD – Point No. 3 | Type CSD – Point No. 2 | Type CSD – Points No. 3 and No. 4 |
| 3.5 (No. 6) | 2.3 | 2.8 | 2.3 | 2.8 | |
| 4.2 (No. 8) | 2.5 | 3.6 | 2.5 | 3.6 | |
| 4.8 (No. 10) | 2.5 | 4.5 | 4.5 | 4.5 | |
| 5.5 (No. 12) | 3 | 3.6 | 4.5 | 3.6 | 5.3 |
| 6.3 (No. 14) | 3 | 4.4 | 6.3 | 4.4 | 6.3 |
Screw protrusion allowance, also known as thread protrusion, is measured from beyond the point of the extreme point of the first full form thread which also includes the drill point length. The protrusion allowance is critical to ensuring adequate thread engagement as well as preventing stripped threads and insufficient damping force.
Incorrect screw sizing doesn’t just lead to mechanical failure—it affects productivity and cost. A screw that is too long can take longer to drive and may require additional torque, increasing wear on power tools and operator fatigue. A screw that is too short might have to be replaced after initial fastening attempts fail, leading to wasted time and materials. Poorly manuafactured screws also play a part in efficiency, be sure to choose products from a reputable supplier, as a working screw is an efficient screw. In projects where thousands of screws are used, these inefficiencies can compound quickly, increasing labor costs and reducing overall profitability.
In many industries—such as construction, infrastructure, and transportation—fastener specifications must meet stringent building codes or engineering standards. Using an incorrect screw size, even unintentionally, can void warranties, result in failed inspections, or lead to liability in the event of structural issues.
Manufacturers often publish load tables and drill capacity charts to help specifiers and installers select the correct TEK screw for each application. Ignoring these guidelines in favor of “just using what’s available” can have serious consequences.
To ensure that TEK screw sizing meets the demands of your project, follow these best practices:
TEK screw size and diameter is far more than a simple specification—they are critical determinants of performance, reliability, and cost-efficiency. Choosing the correct screw size ensures strong, lasting connections, compliance with standards, and optimized installation speed. The wrong size can lead to structural failure, aesthetic issues, increased costs, and even safety hazards. Whether you’re fastening steel sheets on a roof, installing wall cladding, or assembling metal frames, taking the time to select the right TEK screw size is a must for professional results.
As with any component in construction or engineering, precision matters. TEK screws may be small, but when it comes to performance, the right size can make all the difference.