These Forgefix Pozidriv, round head Corrugated Roofing Screws are Zinc plated for increased corrosion resistance. They come complete with a specially designed plastic fold over cap to suit installation of corrugated roofing. The plastic cap has a large surface area to improve weather resistance. Screw size 5.0 x 50mm (Pozi). APPLICATION Suitable for fixing corrugated sheeting to timber sub frames. 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 aluminum and stainless steels by their oxide layers. The Pozidriv screw is similar in appearance to the classic Phillips cross-head, bu