There are different grades of stainless steel screws, and the choice depends on the material they are made from and their durability. Corrseal (corrosion-treated, C4) is usually the most affordable variant and is suitable for e.g. smaller terraces or conservatories where the weather conditions are not particularly challenging. A2 screws are stainless and suitable for e.g. untreated wood. A4 screws are acid-resistant and suitable for demanding environments near the sea or at pools exposed to continuous weather influences.
General recommendations are to use screws, A2 and A4, to avoid rust and increase service life. For outdoor use, non-hardened stainless steel screws (A2 or A4) are particularly recommended due to the increased movement and torque of larger structures. A2 offers some rust protection but can rust in exposed weather areas, and therefore A4 screws are generally recommended for all outdoor areas, except where the building is securely protected, in which case A2 grade may be considered.
