Self-tapping screws are designed to drill their own hole as they are screwed into material, allowing users to perform the two actions at once. Because they create their own fitted threads, self-tapping screws are often used in items that require frequent maintenance.
If working with harder material, it helps to drill a pilot hole before drilling in the self-tapping screw. A pilot hole is drilled with a smaller bit than the screw. A pilot hole isn't necessary when drilling self-tapping screws into soft wood or plastic if the screws have a piercing tip. Other tip types include sharp, flat and blunt.
The two most common types of self-tapping screws are thread-forming and thread-cutting. Thread-forming screws are usually used solely in plastic material. Thread-cutting screws are used with metal and wood. They are designed to hold tightly, but when they are unscrewed, the threads sometimes strip. Metal fasteners installed before the screw can prevent this from happening in projects that need to be taken apart regularly. The fasteners minimize stress as the screw is drilled in.
When choosing a self-tapping screw for the job, it is important to consider the length of the screw tip. The fastener does not create fitted threads unless it can be drilled completely into the material.