Do I need to pre-drill holes for self-tapping screws?

Do I need to predrill holes for self-tapping screws? It depends on both the material the screw is used in, and the type and size of the screws. First, look at the type of screws:

Sharp point self tapping screws are like drywall screws. The hardened steel tip will easily go through a 22 or 24 gauge steel stud, and can be forced through a 20 gauge steel stud, and the fairly coarse threads bite and pull in tightly.
Drill point screws actually have a built in drill bit, and Tech 9 and Tech 7 screws can drill through 1/2 inch steel. These may have Phillips driver heads or hexagon bolt heads.
Self threading machine screws like 12–24 and 1/4–20 have a blunt tip, and are often used for installing door hardware. They have a slot along one edge of the threaded end to discharge bits of metal so they can thread themselves in, but with a blunt tip, they have predrilled doles (the correct size) to be installed.
Depending on which screw, the thickness of the materials you are screwing together, and the type of screw, you may or may not need to predrill the holes for them. It is almost always easier, however, to at least predrill a pilot hole to allow the screws to be installed, especially where accuracy is important.

Take one of the screws and try to drill and tap it into the material that is your base. If it works it works, if not you will have to pre-drill the holes.

When using self-tapping screws I usually pre-drill anyway, the screws start a lot easier and the pilot hole guides the screw so that it doesn’t tilt and go in at a bad angle.

Use a small drill bit the screw will enlarge the hole to the correct diameter.