Drilling capacity guide
How to choose the right drilling capacity for self-drilling screws
Understand drilling capacity before you choose the fastener
Drilling capacity is one of the first checks to make when you are choosing a self-drilling screw for steel. In our catalogue, the drill capacity tells you what thickness range the screw is intended to drill through in the substrate. It is not enough to choose by screw length alone. The substrate thickness must also match what the point is designed to handle.
It is also important to remember that the point cannot drill deeper than its own length. That is why the correct choice depends on both substrate thickness and the fastening family you are using. In some situations, the better option is not a self-drilling screw at all, but a self-tapping screw for a predrilled hole or a sharp-point installation screw for thinner materials.
Where drilling capacity matters in our range
Light section steel and thinner steel combinations
Choose these parts of our range when you are fastening into light section steel or other thinner steel combinations where the difference between 2 x 0.5 mm, 2 x 1.5 mm, 2 x 2.0 mm and 2 x 3.0 mm changes which screw family is suitable. This is where drilling capacity quickly separates lighter framing and roofing fasteners from more demanding steel-to-steel applications.
Heavy section steel
Use our heavy section steel fasteners when the substrate is clearly beyond light-gauge steel and the job calls for screws designed for 4.0 mm and above. This is the right place to compare options for structural steelwork, heavier roofing build-ups and other situations where a light-section screw would be the wrong choice.
See technical details for heavy section steel fasteners on page 25 in the catalogue
Sandwich panels to steel or timber
Choose these sandwich panel pages when the fastener must pass through the panel build-up and still drill correctly into the supporting substrate. Here, panel thickness and substrate thickness work together, so you need to compare both the panel range and the drill capacity instead of treating the screw as a standard sheeting fastener.
See sizes, details and tables for sandwich panel fasteners starting on page 29 in the catalogue
Sandwich panels to concrete
Use our concrete-backed sandwich panel solutions when the job no longer depends on steel drill capacity in the substrate. On this part of the range, the selection shifts to drill diameter and concrete installation logic, which makes it important not to apply steel drill-capacity thinking where the substrate is actually concrete.
See details and tables for sandwich panels to concrete on page 32 in the catalogue
Predrilled self-tapping systems
Choose our self-tapping systems when the application is based on a predrilled hole rather than a drill-point screw cutting its own way through the substrate. These pages are especially useful when you need to compare drill-hole guidance for light section steel, heavier steel and roof-safety or repair-style fastening situations.
See drill-hole guidance for self-tapping systems starting on page 34 in the catalogue
General installation, industrial and ventilation screws
Use these pages when you need quicker comparison across general self-drilling screws, ventilation screws and installation screws. They make it easier to see where drill capacity stays in thinner steel ranges, where stainless options are available and where a sharp-point installation screw is more suitable than a drill-point product.
See details and tables for general drilling-capacity ranges from page 81 in the catalogue
Detailed drilling capacity examples in our catalogue
The catalogue below is the quickest way to compare how drilling capacity changes between different fastening families. Start with page 16 for the core guide, then move into light section steel, heavy section steel, sandwich panels and installation screws to see how the same decision works in different applications.
If the fastener also has to bridge a thicker build-up, compare this page with our guide to clamp length. If the environment is demanding, it is also worth checking corrosion classes before finalising the choice. For installation speed guidance for self-drilling screws, page 102 is also worth checking.
Page 16 - The drilling capacity principle in the product selection guide
Page 22 - Light steel framing screws and roofing/cladding to light section steel
Page 25 - Roofing and cladding to heavy section steel
Page 29 - Sandwich panels to timber
Page 30 - Sandwich panels to light section steel
Page 31 - Sandwich panels to heavy section steel
Page 32 - Sandwich panels to concrete and hammer drill sizes
Page 34 - Self-tapping systems with drill-hole guidance for light section steel
Page 36 - Self-tapping systems with drill-hole guidance for heavy section steel
Page 37 - C-thread self-tapping screws and insulation fasteners
Page 81 - Unidrill pan head self-drilling screws
Page 83 - Univent ventilation screws, including stainless options
Page 85 - Unifix installation screws for timber and thin steel sections
Page 102 - Installation instructions for self-drilling screws and speed guidance
Need help checking the right drilling capacity?
Drilling capacity mistakes are easy to make when the build-up looks simple at first glance but the actual substrate is thicker, harder or different from what was assumed. The risk increases even more when sandwich panels, stainless materials or predrilled fastening systems are involved.
We help customers compare substrate thickness, fastener type, clamp length and installation conditions so the selected reference fits the real job instead of creating problems on site.
What does drilling capacity mean when choosing a self-drilling screw?
Drilling capacity tells you what substrate thickness range the screw point is designed to drill through. When you fasten into steel, that range is one of the first things to check. If the steel is thicker than the point is designed for, the screw is the wrong choice even if the screw length itself looks suitable.
How do I choose between drill capacities such as 2 x 1.0, 2 x 2.0, 2 x 3.0 and 4.0 - 15.0?
Choose by the actual thickness of the substrate you are fastening into, not by what looks close enough. Lower drill-capacity values usually belong to thinner sheet or lighter steel combinations, while higher values are intended for heavier steel sections. Once the substrate moves into thicker structural steel, the fastening family often changes completely.
Is drilling capacity the same as clamp length?
No. Drilling capacity and clamp length solve different parts of the choice. Drilling capacity tells you whether the point can drill the substrate, while clamp length tells you whether the fastener can bridge the full build-up from the outer surface to the inside of the substrate. On many jobs, both values must be correct at the same time.
When should I use a self-tapping or sharp-point fastener instead of a self-drilling screw?
Use a self-tapping or sharp-point alternative when the application is based on a predrilled hole, timber fastening or very thin material where a drill-point screw is not the best fit. That is why it is important to identify the fastening principle first, instead of assuming every steel-related job should be solved with a self-drilling screw.
Why can a self-drilling screw not drill deeper than its own point length?
Because the drill point is the part that creates the hole in the substrate, and its geometry limits how much steel it can penetrate effectively. In practice, that means a screw cannot simply be “forced through” a thicker substrate by using more torque. If the point is wrong for the steel thickness, the fastener choice is wrong.
Do I need to think about installation speed once the drill capacity is correct?
Yes. The drill capacity may be correct, but the installation can still go wrong if the speed is unsuitable. The catalogue includes installation-speed guidance for self-drilling screws, which is worth checking after you have chosen the correct fastening family. That helps the drill point work as intended and reduces the risk of poor installation results.
Can Unite help us choose the right drilling capacity for a specific application?
Yes. We help customers compare substrate thickness, fastening family, clamp length and installation conditions so the selected screw is suitable for the real build-up. That is especially useful when the project mixes different steel thicknesses, sandwich panels, stainless materials or several fastening details in the same job.