... as :Self tapping threads "A","AB", Threads for chipboard screw,wood screw,drywall screw;Type "M","UNC","UNF","BSW"threads for Machine threads.Head ... we are ,we can't jerry-build ,We will actually do strength what you want,testing we can pass.4.Quality ... . "integrity, in accordance with the national standards, do not jerry-build ,all we do for the safety and sake of the user ...