S.Drilling Screw - Nut-Head (2-inch)

Cavalry self-drilling screws, two inches long, with a hex nut head. The extra inch over the standard length is what lets the screw pass through more before it reaches steel: sheet fixed over insulation board or a spacer, thicker timber purlins, double-skin cladding, and profiles with a deep rib where the fixing lands in the trough. Used with a nut setter rather than a bit, so the driver cannot cam out however hard the screw fights on the way through. The point drills its own hole and cuts its own thread in one action, with nothing pre-drilled. Drive at moderate speed and stop when the head seats - running on crushes the washer and dimples the sheet, which is where roof leaks start.