What are the differences between thread formations and drill points?
- Read time: 4 minutes
- Date: 12 Apr 2022
- Sheeting & Cladding
- Rainscreen & Façades
The type of thread formation used on a self-drilling fastener depends on the substrate that is being fixed in to. Two of the most common threads types are:
Isometric thread
Isometric threads which are available in fine and course threads are shaped like an isometric triangle. This thread style is very strong and is resistant to deforming when used with thicker steels during the tapping process. For this reason, fasteners with this type of thread are particularly good for use with heavy section steel. An isometric thread is a good all-rounder and is the most frequently used thread formation. However, in some applications particularly in thin section for flat roofing it doesn’t provide as good a performance as a buttress thread.
Buttress thread
Buttress threads are shaped with a flat surface on the upper side of the thread. The flat thread surface prevents the fastener from working loose as the structure it is securing moves due to the expansion and contraction of materials or wind load. Buttress threads are used for fixing into light steel, thin steel sheets and plywood.
What are the differences between drill points?
Drill points are specifically engineered to facilitate effective drilling into a variety of substrates and materials such as light steel, heavy steel, aluminium, or timber.
Common drill point designs include:
S point
An S point drill bit incorporates a long sharp point with a flute designed to disperse the metal swarf. This design of drillpoint is particularly suited for attaching thin metal sheeting to timber substrates. Within the industry they are also known as ‘slash’, ‘gash’ or ‘Type 17’ point screws.
Reduced point
A fastener incorporating a reduced point is typically used for attaching the material to thin metal sheet or stitching (joining) two thin sheets together. The diameter of the drillpoint is significantly reduced in comparison to the threads which maximises pull out performance.
Light steel drillpoint
Light steel drillpoints are designed to drill through cold rolled steel between 1.2mm and 3mm thick. Common applications include the attachment of metal sheeting, composite panels and timber to the building structure. It’s common to find additional steel sections within these applications and this can increase the thickness of steel needing to be drilled. For this reason, some light steel drillpoints have a drilling capability of up to 5mm.
Heavy steel drillpoint
Heavy steel drillpoints feature an extended flute drill point for use with thicker hot rolled steel sections between 4mm and 12mm thick. The longer drillpoint enables the swarf to be removed easily and the drilling operation to be completed before the thread is engaged in the substrate.
Super heavy steel drillpoint
A super heavy drillpoint has a twisted drill point which is capable of drilling hot rolled steel up to 25mm thick. Typical applications include attaching material to the main steel stanchions of a portal frame.
Working together
A well-engineered self-drilling fastener takes into account both the thread formation and the drillpoint design to ensure that they work together to give the best performance for the given application.
