A set screw is a type of screw generally used to secure an object within or against another object without using a nut. The most common examples are securing a pulley or gear to a shaft. Set screws are fully threaded and has no head projecting past the major diameter of the screw thread. These set screws are driven with an internal-wrenching hex socket drive. Features: These set screws are made from 12.9 grade carbon steel for high hardness, durability and long service life. Oxidation surface finishing provides these set screws a cover of rust and corrosion protection. They are multipurpose hex socket head set screws that you can simple drive with a hex key. There are 8 common sizes and you can concentrate on your project without worrying about not having the correct screws. Get these total 200 pieces screws so you won't be running off to the hardware store for a set screw for quite a while. Specifications: Material: 12.9 grade carbon steel Surface Finishing: Oxidation Color: Black Size and Quantity: M3x3mm 25pcs M3x4mm 25pcs M3x5mm 25pcs M3x6mm 25pcs M3x8mm 25pcs M3x10mm 25pcs M3x12mm 25pcs M3x14mm 25pcs Package Includes: 200pcs x Screws