Self tapping screws are normally used with sheet metal and plastics. These have a countersunk head AKA flat head with a pozi (cross recessed) drive. They are typically used in conjunction with a countersunk hole providing a flush, snag free fit. As the name suggests, this type of screw forms its own thread as it is installed into a pre-drilled hole. Not to be confused with self drilling screws, the main difference is that self-tapping screws cannot go through metal without a pilot hole, which must be pre-drilled or pre-punched. Exact drill or punch hole size is also important. The screw will become loose and not thread properly and securely if the hole’s too big. If the hole’s too small, the screw can break or cause the material to split or crack. Self-tappers are good for use with metals, various types of plastics (plywood, fiberglass, polycarbonates), and cast or forged material, like iron, aluminium, brass or bronze. Self-tapping screws also work for surfaces where you can’t secure the rear end with a nut. Common applications include fastening aluminium sections, attaching metal brackets onto wood, or inserting screws into plastic housings. This set contains a selection of of No.4, No.6 and No.8 (3.5mm, 4.2mm & 4.8mm thread diameter) screws. A2-70 stainless steel, also known as 304 or 18/8 grade has great weather resistance and longevity. It can be used in all outdoor conditions apart from where consistent exposure to either salt water or sewerage is expected.
