Industrial Fasteners Institute Standard IFI-113

• Cold heading quality steel wire 0.189 - 0.183 in Dia major 0.141 - 0.135 in Dia minor

Several common methods such as rivets, screws, and spot welding are used to fasten materials to ductwork. Three types of screws are most often used. The first is self-tapping only and requires a hole to be drilled before the screw can be utilized. The others are both self-tapping but also create their own holes. Self piercing screws have very sharp points which act much like a scratch awl in making a small opening in the steel for the threads to engage and work the sheet metal into a coned threaded hole. These work well for light gage steel. Self-drilling screws have an integral drill point which creates a large hole for tapping. This allows the screws to be used on heavy gages of steel. The maximum total thickness of steel that the self-drilling screw can be used with is determined by the drill point.