Self Drilling vs Self Tapping Screws
A self drilling screw has a drill point and makes its own hole in steel; a self tapping screw forms a thread in a hole you have already drilled. Use self drilling screws for roofing and steel framing, self tapping screws for sheet metal and plastics.
How self drilling screws work
The tip is shaped like a drill bit. It bores through the steel, then the thread follows and taps the hole, so drilling, tapping and fixing happen in one step with a screw gun.
How self tapping screws work
The screw goes into a pilot hole that is slightly smaller than the thread. Its hardened thread cuts or forms a mating thread in sheet metal, plastic or soft metal.
When to use which
- Roofing sheets, purlins, light steel framing: self drilling
- Appliances, enclosures, plastic parts: self tapping
- Thin sheet where a pilot hole is easy: either
Coating and material
Outdoors and near the coast, use ruspert coated or bi-metal stainless self drilling screws, because plain zinc plated screws rust quickly.
