Clamp length guide
How to choose the right clamp length for screws and sandwich panel fasteners
Understand clamp length before you choose the fastener
Clamp length is one of the quickest ways to check whether a fastening suits the full build-up you are working with. In our catalogue, it helps you move beyond nominal screw length and focus on the actual thickness the fastener must bridge before it anchors correctly in the substrate.
For self-drilling screws, the clamp length is measured from the outer surface to the inside of the substrate. That means you should include the outer sheet, any intermediate board or panel build-up, and the substrate itself. In thicker assemblies, clamp length should also be checked together with drill capacity and the specific fastening system.
Where clamp length matters in our range
Start with the clamp length principle
Use our clamp length guidance as the first check when you need to confirm whether the fastener can bridge the full build-up from the outer surface to the substrate. This is the core CL logic in our catalogue and it helps prevent choosing a screw by nominal length alone.
Roofing and cladding with intermediate board
Choose by clamp length range when an intermediate board sits between the outer sheet and the supporting steel. These assemblies step up quickly, so the working range in the table is the safest way to match the screw to the real build-up.
See clamp length examples for roofing and cladding with board on page 28 in the catalogue
Sandwich panels to timber
Use the panel thickness guidance as your starting point when fastening sandwich panels to timber. These jobs often require much longer fasteners than standard sheeting work, so the correct reference depends on the full panel build-up, not only on the outer sheet.
See sandwich panel to timber examples on page 29 in the catalogue
Sandwich panels to light section steel
Check the table carefully when fastening sandwich panels to light section steel, because the clamp length range can move from relatively modest build-ups to very thick panel assemblies. This is where CL becomes one of the fastest ways to shortlist the right reference before you compare drill capacity.
See sandwich panel to light section steel tables on page 30 in the catalogue
Insulation screws and special systems
Do not assume every insulated assembly follows a simple min-max clamp length span. Some insulation fixings use a system rule instead, such as a maximum clamp length derived from screw length, so this part of the range should always be checked in the relevant table.
See insulation screw clamp length logic on page 38 in the catalogue
Detailed clamp length examples in our catalogue
The catalogue below is the quickest way to compare how clamp length guidance changes between different fastening families. Start with page 16 for the core principle, then move into the thicker build-ups on pages 28-32 and the insulation-related tables on pages 38-41.
If your choice also depends on how much steel the drill point can penetrate, compare this page with our guide to drilling capacity. If the project environment is demanding, it is also worth checking corrosion classes before finalising the fastening.
Page 16 - The clamp length principle in the product selection guide
Page 28 - Roofing and cladding + board to light 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
Page 38 - Insulation screws and max clamp length logic
Need help checking the right clamp length?
Clamp length mistakes are easy to make when the assembly includes intermediate layers, thicker panels or insulated build-ups. A screw that looks long enough at first glance may still be the wrong choice once the full build-up and substrate are counted correctly.
We help customers compare clamp length, drill capacity and fastening family so the selected reference fits the real installation instead of creating rework on site.
What is clamp length?
Clamp length is the thickness the fastener needs to bridge from the outer surface to the inside of the substrate before it anchors correctly. It is a practical selection value that helps you match the fastening to the real build-up instead of relying only on nominal screw length.
Do I count both the outer sheet and the substrate in the clamp length?
Yes. In our catalogue, the clamp length is measured from the outer surface to the inside of the substrate. That means the outer sheet, any intermediate layer and the substrate must all be included when you check whether the fastening is suitable.
Is clamp length the same as drill capacity?
No. Clamp length tells you how much material the fastener needs to bridge, while drill capacity tells you what thickness of steel the drill point can penetrate. Both must be correct, especially when fastening into steel sections or thicker sandwich panel assemblies.
Why does clamp length matter more in sandwich panels and board build-ups?
Because those assemblies create a much thicker build-up than standard sheeting work. Once you add an intermediate board or a full sandwich panel, the required fastener length can increase quickly, so the clamp length table becomes one of the fastest ways to narrow down the correct reference.
Why do some tables show a min-max clamp length while others mainly show a maximum value?
That depends on the fastening family and how the product is presented in the catalogue. Some products are listed with a clear working clamp length range, while others are shown by maximum panel thickness or system logic. The important part is to follow the table for that exact fastening type rather than assuming every product is presented in the same way.
Can Unite help us choose the right clamp length for a specific build-up?
Yes. We help customers check the full assembly thickness, substrate and fastening family so the selected reference fits the real installation. That is especially useful when the job includes intermediate boards, sandwich panels, insulation systems or other thicker layered build-ups.