Self tapping screws are specially designed screws which produce their own mating thread into the material used as they are being applied into a pre-drilled or punched or moulded holes.
Mainly used in thin sheet material they can also be used in some soft plastics and Aluminium.
Main advantages are easier and quicker assembly (no holes to tap as with machine screws) good resistance to vibration due to closeness of thread engagement and access is only required from one side.
Standard self tapping screws have a pointed end (Gimlet point) Type AB (Form C) which gives a lead into the hole provided. A limited range is also available with a blunt end Type B (Form F) these are mainly used in blind hole applications such as Aluminium castings etc.
Drives available tend to be Pozidrive cross recess or 6 lobe TX drive. Slotted drives are still available on request but supplies can be difficult as the former drives are more popular due to ease of automatic assembly and driver slippage (Cam out)
Common Head styles are Pan, Countersunk, Raised Countersunk.
Hexagon head type also available. A cylindrical Socket (allen key) drive is also available in a limited range of sizes.
As well as the standard self tapping thread forms another type is available known as a thread forming screw. These screw into a pre-drilled hole and form an actual recognised screw thread similar to that provided by a separate machine tapping operation ie M4, M5 etc.
Lastly there are screws known as Self Drilling Screws. These screws have an integral drill point on the end. They then both drill tap a thread into Aluminium in one operation.