Self drilling screw 4.2 x 19mm znk

A self-drilling screw is needed, for example for:

- Attaching the auxiliary supports to the column
- Attaching the top system bracket to a post (not mandatory, but helpful)
- Attaching a cable tray bracket to any location on the pole
- Attaching a cable tray 30x20mm (included with the cable tray 30x20)