These Forgefix Phillips, single thread Drywall Screws have a black phosphate finish for increased durability. The screws come complete with a Phillips No.2 insert bit. Their Bugle Head allows the screw to sink effortlessly into the dry lining without the need for countersinking, which in turn minimises the damage to the surface. Designed for fitting dry linings to studding. Phosphate coatings are made up of thin crystalline layers of phosphate compounds that adhere to the surface of the fixing or fastener. The phosphate crystals are porous and can be formed from zinc, manganese, or iron phosphate solutions. Phosphate coatings offer good corrosion resistance and have an excellent ability to absorb supplementary coatings which improves appearance, corrosion resistance and resistance to abrasion. The Phillips screw has four simple tapered slots. It is designed so that a Phillips tip screwdriver can turn a Phillips screw with increasing torque. When the torque gets to be too strong for the tip then the screwdriver tip winds itself out of the screw thus preventing over-tightening and or damage to the screw head. Coarse thread screws (mainly drywall screws) have an extremely sharp point and are designed to penetrate plasterboard skin. The coarse thread eases in to the board then the timber baton holding the board firm.