These Forgefix Pozi Carcass Screws have an extremely coarse single thread. The have a black phosphate coating for increased durability and a self drill point for easy installation. APPLICATION: Designed specifically for chipboard and MDF (medium density fibre) board and carcass assembly. 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 Pozidriv screw is similar in appearance to the classic Phillips cross-head, but in fact is very different. The Pozidriv has four additional points of contact, and does not have the rounded corners that the Phillips screw drive has. The biggest advantage it offers is that, when used with the correct tooling in good condition, it does not cam out, allowing great torque to be applied. The Pozidriv screw can easily be distinguished by a line embossed in the screw head at 45° to the slots for the driver. Coarse thread 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.