The partial thread extends over only part of the length of the screw. Partially threaded screws are particularly suitable for fixing wooden boards to wooden beams. The non-threaded part should always be selected so that it corresponds to at least the thickness of the board to be screwed into place. The thread tightens securely into the lower piece of wood, while the upper piece of wood is held tightly against the lower piece by the screw head.
For SPAX screws up to 100 mm in length, the following rule of thumb can be used to calculate the screw length required for connecting two pieces of wood, e.g. in deck construction:
The screw length (Ls) depends on the thickness of the cover board (t).
Formula: Ls = 2.5 x t
Example: Ls = 2.5 x 24 mm => Ls = 60 mm