These Forgefix Pozi Compatible Machine Screws are designed for use with nuts or pre-tapped holes. They are Zinc plated for increased corrosion resistance. The countersunk head is suitable for pre-countersunk holes or when fastening to timber to leave a flush surface. APPLICATION:Ideal for use in many DIY, ironmongery, 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 aluminum 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. A Machine screw is generally a smaller fastener, threaded the entire length of its shank that usually has a recessed drive type (Slotted, Phillips, etc.). Countersunk heads are designed to sink flush with substrates to leave a smooth surface finish.