Steel screws are made of alloy steel and have high tensile strength after heat treatment. Stainless steel socket head screws are usually made of 302 or 304 and are not heat treated. There are many types of screws. The design material and thread type of these screws vary according to their use and the material to which they are intended to be joined. Machine screws are common and common types of screws, designed with straight, non tapered shank and blunt ends. Mechanical screws are designed for pre threaded holes or for use with nuts. These screws are usually used for manual or electric screwdrivers. Plastic screw has different design from ordinary machine screw. These screws are made of fine threads and are suitable for softer materials. These screws can be installed through the plastic with a stress and low torque of. The design screw does not crack or crack the base plastic material. Sheet metal screws, also known as self tapping screws, are used for function and design. Depending on the needs of the metal, their heads can be flat, oval or hexagonal. Sheet metal screws have sharper threads than other screws, allowing them to be cut into hard material. Ball screw pair Their design includes a reinforced thread that is harder than the metal they are used to screw in, allowing the internal thread not to break when driven into a material softer than the screw material. Another type of screw, the socket and the shoulder screw, provides space between the surfaces. The screws are made of strong metals such as steel and stainless steel and consist of a head, thread and shoulder.