What do the wings on the tip actually do?
They ream a slightly wider hole through the timber. That clears the wood so the screw reaches full RPM without the friction burning it. As soon as the wings hit the steel they break away. From there the thread self-taps straight into the metal and clamps the timber down.
How thick can the timber be?
These suit timber from 64mm up to 78mm. 78mm is the maximum fixture thickness. Pick a length that still leaves plenty of thread to bite into the steel underneath.
Do I need to pre-drill or use a pilot hole?
No. The No.3 self-drilling tip cuts through the timber and the steel on its own. Line it up and drive it straight in.
What's the maximum steel thickness?
Up to 5.0mm of light section steel. Go thicker than that and the tip can't clear the metal cleanly, so keep within the 5.0mm limit.
What speed should I run the driver at?
Keep the drill between 1,000 and 1,800 RPM. That's quick enough for the tip to cut without cooking the timber or blunting the point.
Are these OK for outdoor use?
This silver zinc version is Corrosion Rating 1, so it's for interior, dry, low humidity spots. For exposed or damp work, go for an exterior-rated wing-tip screw instead.