At Fabory, self-tapping screws are divided into several categories. Besides technically considering wood screws as self-tappers, we have made a distinction between; sheet metal screws, thread-forming screws, and self-drilling screws.
• Sheet metal screws are screws for thin sheet material. They have a sharp point that indents and displaces the material, creating a protrusion on the backside of the sheet. The advantage of this protrusion is that threads are also formed in it, maximizing the contact surface between the screw and the sheet. This connection can withstand a relatively high tensile force.
• Metric thread-forming screws. These are screws with a metric thread that are provided with a surface hardening. This makes the surface harder than the material into which it is screwed, causing the screw to deform the base material. No chip formation occurs here, making this often used in electrical engineering applications.
• Thread-forming screws. In this group are thread-forming screws intended for use in plastic applications. We distinguish between a 45° entry angle, a 30°, and an 8° top angle. A significant advantage of a 30° top angle is that it creates a larger contact surface with the material. This results in a higher pull-out value in soft materials. A 45° top angle is often used in more rigid plastics because the plastic cracking risk is smaller than with a sharper top angle. A small indication is the softer the material, the sharper the top angle.
• Self-drilling screws are screws with a drill point. These remove the material to the core diameter and then cut their thread. Like sheet metal screws, they are used in thin sheet material, but especially when a protrusion on the back is not desired.