Product code 29447/1 Description 40mm Gyproc Drywall Screws are corrosion resistant self-tapping screws, which have a black finish and are not only Fine thread but coarse thread as well. They are ideally suited for the fixing of boards to drywall metal framing which is less than 0.8mm thick. The length of the drywall screw selected should be sufficent to give a minimum penetration of 10mm into the drywall section.