Product instruction：A screw,Website: , or bolt, is a type of fastener, typically made of metal, and characterized by a helical ridge,known as a male thread (external thread) or just thread, wrapped around a cylinder. Some screwthreads are designed to mate with a complementary thread, known as a female thread (internal thread),often in the form of a nut or an object that has the internal thread formed into it. Other screwthreads are designed to cut a helical groove in a softer material as the screw is inserted. The most commonuses of screws are to hold objects together and to position objects.A screw will almost always have ahead on one end which contains a specially formed shape that allows it to be turned, or driven, with atool. Common tools for driving screws include screwdrivers and wrenches. The head is usually largerthan the body of the screw, which keeps the screw from being driven deeper than the length of thescrew and to provide a bearing surface. There are exceptions; for instance, carriage bolts have adomed head that is not designed to be driven; set screws often have a head smaller than the outerdiameter of the screw; J-bolts have a J-shaped head which is not designed to be driven, but rather isusually sunk into concrete allowing it to be used as an anchor bolt. The cylindrical portion of the screwfrom the underside of the head to the tip is known as the shank; it may be fully threaded or partiallythreaded.Place of Origin:Zhejiang, China (Mainland) Brand Name:ZC  Standard:DIN 7982Material:Carbon SteelFinish:Blue Zinc Plate Surface treatment:Heat Treating： Type: PHILLIPS CSK HEAD Color:Zinc White Packing:Carton Item:China Fastener Application:Building Packaging Details:Small box, carton, pallet, nylon bag, for self drilling screwProduct Description1. Grade: C1022 2. Size: ST3.5, ST3.9, ST4.2, ST4.8, ST5.5,ST6.33. Length：13-120mm4. Standard: DIN 5. Certification: ISO9001, CEProduct Name:Self tapping screw Material: Carbon steelUsed:building industry machinery