These forgefix multi purpose pozi 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 applicationsuitable 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 actin