These Forgefix Pozidriv Self-Tapping Screws have countersunk heads and are Zinc Plated for increased resistance to corrosion. They tap their own thread in to a pre-drilled pilot hole in sheet or solid material. They are single threaded to resist pull-out. APPLICATION: Ideal for use in many DIY, ironmongery, engineering, electrical and plumbing applications. Zinc coatings prevent oxidation of the protected metal to create a longer lasting finish. It does this by forming a barrier and by acting as a sacrificial anode if this barrier is damaged. Zinc oxide is a fine white dust that (in contrast to iron oxide) does not trigger a breakdown of the substrate’s surface integrity as it is formed. The zinc oxide, if left intact, can act as a barrier to further oxidation, in a way similar to the protection afforded to aluminium and stainless steels by their oxide layers. 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. Countersunk heads are designed to sink flush with substrates to leave a smooth surface finish.