These Forgefix Multi-Purpose Pozi Compatible Screws with countersunk heads have a zinc finish for increased durability. The screws are immensely popular and versatile, and used in all trades including joinery, electrical and plumbing. Also widely used in DIY applications. APPLICATION Suitable for use with many materials including PVCu, Timber, Chipboard, MDF, and other similar types. 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&rsquos 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. The countersunk head is designed to sink flush with substrates to leave a smooth surface finish. They have single threads, designed to offer higher pull out values and quicker insertion. Multi-Purpose Pozi Screw CSK ST ZP 4.0 x 40mm Forge Pack 20