... drywall screw;Type "M","UNC","UNF","BSW"threads for Machine threads.Head typesHexagon head,Mushroom head,Pan head,Countersunk head ... ,chromium plated,Tin plated,Black phosphating ,anodized ,Parkerising,and Environmental Plated is used in our products,Hexavalent chromium are accord ... used in most of places such as drywall,concrete,chipboard,machine,wood...2) Main export market:North America,South America ...