Coarse threads have a lower thread pitch, therefore fewer threads per inch (TPI). They are designed for stitching sheets and fastening cold rolled purlins or timber.
Fine threads have a higher thread pitch, therefore more threads per inch (TPI). They are designed for fastening hot rolled purlins and thicker steel applications. They have greater pull out values because there are more connection points with the substrate.
Our longer fixings have high threads just under the head of the fixing. These threads are always coarse in order to engage the outer sheet of an insulation panel. The diameter is slightly wider than the thread at the tip of the fixings to ensure engagement with the hole that has already been created.
On our insulation panel fixings, there is an unthreaded portion of the screw between the high thread and the main thread.