S.Drilling Screw - Nut-Head (3-inch)

Cavalry self-drilling screws, three inches long, with a hex nut head - the longest self-driller on our shelf. Length here is entirely about what the screw must pass through before it finds steel: sheet over thick insulation, deep-profile roofing where the fixing lands in a high rib, sheet over battens or a spacer frame, and double-skin systems with a cavity between. Anything shorter simply will not reach purlin. Driven with a nut setter rather than a bit, so it cannot cam out however hard it works on the way through, and the point drills its own hole with nothing pre-drilled. At this length the screw wants to wander as it starts, so hold the driver square and let the point cut before applying real pressure.