Screws for mounting sandwich panels to a concrete structure require pre-drilling with a 5.0 mm or 5.5 mm drill bit!
If the concrete is weaker (for example, old concrete during reconstruction), it is pre-drilled with 5.0mm drill bit. If it is stronger (typical case - new construction) the 5,5 mm drill bit is used.
A characteristic of specialized sandwich panel screws is that they have a thread under the head that is larger in diameter than the main one (6.8 mm vs. 6.3 on the main one). The wider 6.3 mm thread ensures a good compression of the EPDM on the washer and the hole becomes watertight. Even on a wall, a screw without a support thread is a prerequisite for the penetration of up to 4 l of water through one hole, during a summer storm, for example.
The screws for BAUFIX sandwich panels are not only zinc-coated, but also have an additional anti-corrosion coating, which guarantees their up to 10 times longer life.
The screws are 5/16 or 8mm hexagonal drive. A 5/16 tip is recommended because it prevents wobling. This is also ensured by the higher profile of the head. Thus, the screw is retained in the tip and facilitates installation in hard-to-reach places.